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Abstract

Insulin resistance is prevalent in women with polycystic ovary syndrome (PCOS), and plays a critical pathophysiologic role in both the metabolic and reproductive complications of PCOS. This review focuses on the contribution of insulin resistance to anovulation in PCOS and to the high risk for Type 2 diabetes, metabolic syndrome and early cardiovasular disease. Key points for clinicians emphasized by this review are the following: PCOS is a clinical diagnosis and alternative diagnoses must be excluded; PCOS carries an inherent risk of insulin resistance and, hence, metabolic consequences for which women with PCOS should be screened regardless of BMI or degree of obesity; and PCOS is associated with infertility and this should be discussed early on in care of women diagnosed with PCOS, recognizing that there are several possible strategies to address infertility in women with PCOS, each with its own risks and benefits.

Keywords

cardiovascular disease risk infertility insulin insulin resistance metformin PCOS

Evolution of a definition

In 1935, Stein and Leventhal described the association of oligo- or amenorrhea, hirsutism and obesity with polycystic ovaries, labeling this the Stein–Leventhal syndrome [1]. This syndrome was initially defined as chronic anovulation associated with androgen excess, phenotyped as women with hirsutism, seborrhea, acne and alopecia, and, rarely, virilization. Presence of all phenotypic features simultaneously was required to meet the diagnosis of Stein–Leventhal syndrome, and treatment consisted primarily of bilateral ovarian wedge resection.

Subsequently it came to light that both obese and lean women with certain – but not necessarily all – of the above features were presenting to clinicians, prompting a reevaluation of the syndrome and resulting in a new syndrome called the polycystic ovary syndrome (PCOS) with an expanded definition. Advances in technology over time, including means of measuring serum gonadotropins and sex steroid levels; the application of ultrasound imaging to ovarian tissue; recognition of the presence of insulin resistance as a feature of this syndrome; recognition of hereditary differences in degree of sensitivity to circulating androgens by target tissues; and association and linkage analysis studies indicating that PCOS is a multifactorial polygenic disorder, have further expanded the definition. It became evident that women with PCOS could be obese or thin, with a range of androgen-related cosmetic issues.

The diagnosis of PCOS is ultimately a clinical one, and no one specific test is diagnostic of the syndrome. The most commonly cited definitions of PCOS are those drafted at the NIH in 1990, commonly referred to as the NIH Expert Conference, and the subsequent statement issued from Rotterdam in 2003. The NIH Expert Conference [2] definition of PCOS requires that all of the following criteria be met: clinical hyperandrogenism and/or biochemical hyperandrogenemia; chronic oligo- or anovulation; and exclusion of other causes of androgen excess or oligoovulation, such as hyperprolactinemia, hypo-or hyperthyroidism, congenital adrenal hyperplasia and hypercortisolism. In contrast, the Rotterdam criteria of 2003 [3] designates as PCOS, after exclusion of differential for hyperandrogenism and oligoovulation, whenever two out of the three following criteria are met: first, chronic oligo- or anovulation; second, clinical and/or biochemical hyperandrogenism; OR third, anatomically polycystic ovaries on ultrasonographic imaging. The Rotterdam definition is in effect more inclusive. It includes all women who would be diagnosed by the NIH criteria, but also adds two new phenotypes: women who are ovulatory but have polycystic ovaries and hyperandrogenism, and oligo- or anovulatory women with polycystic ovaries but without clinical or biochemical signs of hyperandrogenism. This expansion of the definition and inclusion of two new categories of women with PCOS have led to some controversy as to the clinical implications of the syndrome [4]. Specifically, perhaps not all phenotypes carry the same metabolic and vascular risk association. One must also keep in mind that anovulation, of any cause, may lead to polycystic ovaries on ultrasound evaluation in 75% of those evaluated [5], and that ˜23% of normal volunteers without any menstrual disturbance had polycystic ovaries on ultrasound, more commonly in younger women [6].

The Androgen Excess Society guidelines sought to arbitrate the above controversy and proposed that the definition of PCOS be similar to the Rotterdam criteria, with the caveat that hyperandrogenism must be present [7], stating that PCOS is distinguished by the presence of hyperandrogenism.

For the clinician evaluating an individual patient for the diagnosis of PCOS, it is critical to start with a thorough history and physical examination, and obtaining serum total and free testosterone and DHEA-sulfate levels to evaluate for hyperandrogenemia and screen for androgen-secreting ovarian or adrenal tumors. Tests to exclude other causes of oligoovulation or androgen excess should also be obtained, such as serum prolactin, 17α-hydroxyprogesterone (to exclude non-classical congenital adrenal hyperplasia), thyroid-stimulating hormone (TSH) and in cases where warranted by clinical suspicion testing to exclude Cushing's syndrome (either a 24-h urine collection for creatinine and free cortisol, or a 1 mg overnight dexamethasone suppression test). In cases of oligo/anovulation without clinical or biochemical signs of hyperandrogenism, consideration should be given to obtaining a pregnancy test and serum estradiol, follicle-stimulating hormone (FSH) and luteinizing hormone (LH) to exclude premature ovarian failure or functional hypothalamic amenorrhea.

Metabolic consequences of PCOS

Insulin resistance in PCOS

One of the earliest reports linking insulin resistance to PCOS was the 1921 treatise by Emile Achard and Joseph Thiers on the diabetes of bearded women (i.e., diabète des femmes à barbe). Decades later, the observation in 1976 that young women who are hyperinsulinemic due to a genetic defect in the insulin receptor are also virilized led to the concept that insulin may play a critical role in PCOS [8,9]. Further study of PCOS women demonstrated a positive correlation between serum concentration of fasting serum insulin and of testosterone and androstenedione [10]. It has since been demonstrated in cultured human ovarian tissue that insulin stimulates ovarian testosterone production by theca cells from women with PCOS [11], and in vivo studies have demonstrated that suppression of insulin release in women with PCOS reduces ovarian cytochrome P450c17α activity [12] and circulating testosterone levels [13]. Further, IGF receptors have been discovered in ovarian cells which also produce IGF-binding proteins. IGF-1 and IGF-II, structurally related to insulin, similarly participate in normal follicle development [14,15]. These observations support the idea that in women with PCOS hyperinsulinemia stimulates ovarian androgen production and contributes to the hyperandrogenemia. Figure 1 is a proposed schema in which insulin resistance, in the setting of predisposing genetic factors, is a critical driver of hyperandrogenism. To this day, however, the directionality of events – that is, whether hyperinsulinism causes hyperandrogenism, vice versa, or both – remains to be fully elucidated.

Figure 1.

Insulin resistance in polycystic ovary syndrome, effects on ovarian androgen production.

Role of insulin resistance in androgen excess in PCOS

Several lines of evidence support the idea that insulin resistance and its compensatory hyperinsulinemia are intrinsic to the PCOS state and play a key role in producing the androgen excess of PCOS. First, women with PCOS who have undergone either partial [16] or total [17] oophorectomy, or have been treated with a long-acting gonadotropin-releasing hormone agonist to supress pituitary LH and FSH release [18,19], still remain insulin-resistant despite a hypoandrogenic state. Also, girls who are pre-pubertal can have symptoms of hyperinsulinemia with acanthosis nigricans years before elevations in serum androgens appear [20], suggesting that the insulin resistance may precede the hyperandrogenism of PCOS. Finally, normal men have significantly higher androgen levels than women with PCOS but do not demonstrate the insulin resistance or hyperinsulinemia typical of PCOS [13].

Sex hormone-binding globulin (SHBG) is the primary binding protein for testosterone, and it is the unbound testosterone (also called free testosterone) that acts on target tissues. Insulin is thought to increase circulating levels of free testosterone by two specific mechanisms: first, by stimulating ovarian biosynthesis and secretion of testosterone, and, second, by directly suppressing hepatic production of SHBG.

Regarding insulin's stimulation of ovarian testosterone production, in vitro studies have demonstrated greater stimulation of testosterone production by human theca cells obtained from women with PCOS compared with theca cells obtained from normal women, and insulin has been shown to inhibit hepatic production of SHBG both in vitro [21] and in vivo [22]. In vivo studies in which hyperinsulinemia was induced resulted in increases in circulating androgens in women with PCOS but not in normal women, both independently of gonadotropin release [23], and independently of BMI [24]. Conversely, administration of diazoxide to inhibit insulin release in obese women with PCOS resulted in a decrease in serum total and free testosterone levels with no change in gonadotropin level, suggesting a direct effect of insulin to stimulate ovarian testosterone production [13]. A similarly designed study of administration of diazoxide to normal non-obese women without PCOS found no effect of diazoxide on circulating serum testosterone concentrations [25], suggesting that women with PCOS have an inherent susceptibility to the hyperandrogenic effects of insulin.

With regard to insulin's suppression of hepatic production of SHBG, in vitro insulin has been shown to inhibit SHBG production by cultured HepG2 cells [21], and, in vivo, administration of diazoxide to pharmacologically castrated women with PCOS resulted in an increase in levels of SHBG despite no change in sex steroids [22].

Finally, it is noteworthy that studies of women with both Type 2 diabetes (DM2) [26,27] and Type 1 diabetes, including lean patients, [28 –31], reported a higher prevalence of PCOS in these women than in the general population. This suggests that insulin resistance, or more specifically hyperinsulinemia (whether endogenous or exogenous), is responsible for the ovarian hyperandrogenism in these diabetic patients.

Prevalence of insulin resistance in women with PCOS

Insulin resistance is observed independently of obesity in women with PCOS, and it is critical for physicians treating women with PCOS to bear in mind that both obese and lean women with PCOS demonstrate hyperinsulinemic insulin resistance, independently of their adiposity [32,33]. In 1989, Dunaif et al. [34], using the hyperinsulinemic-euglycemic clamp technique to measure whole-body insulin sensitivity, demonstrated that both obese and lean women with PCOS were significantly insulin-resistant compared with their weight-matched normal controls, with lean women with PCOS being as insulin-resistant as obese normal women, and obese normoglycemic women with PCOS being as insulin-resistant as DM2 women. In this study, PCOS status and obesity synergistically reduced insulin sensitivity – that is, insulin sensitivity was greatest in lean normal > lean PCOS = obese normal > and worst of all in obese PCOS women, so that having both PCOS and obesity worsened insulin resistance in a complementary fashion [34]. A take home point is that insulin resistance is a frequent feature of PCOS regardless of BMI.

Methodologies to test accurately for insulin resistance remain technically challenging and are not used in clinical practice. However, there are several clinical parameters that reflect underlying insulin resistance, including obesity, increased waist-to-hip ratio, presence of acanthosis nigricans, low HDL-c level, elevated triglyceride level, and reduced serum SHBG. One clinical consequence of insulin resistance is impaired glucose tolerance (IGT) and, more severely, overt DM2. In two prospective trials of women with PCOS conducted in the USA [35,36], there was a 31–35% prevalence of IGT and a 7.5–10.0% prevalence of DM2 in young to middle-aged women with PCOS. In a prospective, controlled trial over a 2–3-year follow-up, among women with PCOS there was at baseline a 37% prevalence of IGT and 10% prevalence of DM2, with a subsequent 16% conversion/year from normal glucose tolerance (NGT) to IGT and a 2% conversion/year from IGT to DM2. Consistent with these observations, in the Nurses' Health Study II (NHSII) of 101,073 women followed for 8 years, the conversion rate to DM2 was approximately twofold higher in oligomenorrheic women, independent of weight, than those with normal menses [37].

Collectively, studies indicate that in the USA there is a 10-fold increased prevalence of DM2 in young women with PCOS, and that 30–50% of obese women with PCOS develop IGT or DM2 by the age of 30 years old (earlier than their peers without PCOS). Of note, abnormalities of carbohydrate metabolism, resulting in IGT or DM2, tend to cluster in first degree relatives of women with PCOS [38,39]. Similar to patients with DM2 without PCOS, in patients with PCOS a positive first degree relative with DM2 correlates significantly with the risk of having DM2 [40]. In short, women with PCOS have been found to be at substantially increased risk of developing DM2 [35].

Detection of glucose intolerance in women with PCOS

Neither insulin resistance nor biochemical evidence of glucose intolerance is necessary for the diagnosis of PCOS. Moreover, many women with PCOS will have demonstrable insulin resistance with no clinical evidence of glucose intolerance. Nonetheless, given the evidence above of a high prevalence of glucose intolerance and DM2 in PCOS, it behooves clinicians to screen for these disorders at the time of PCOS diagnosis. Expert opinion would recommend screening all women with PCOS for glucose intolerance at the time of diagnosis using a 2–h 75-g oral glucose tolerance test (OGTT) (regardless of BMI) and repeat screening at 2–5 year intervals [41,42]. An OGTT is the recommended screening test for glucose intolerance, since, as noted below, studies indicate that in women with PCOS the fasting serum glucose and HbA1c levels may be in the normal range even when a woman with PCOS has IGT or DM2 when assessed by an OGTT [43 –45].

In women with PCOS, the OGTT remains the gold standard test for screening for glucose intolerance. Legro et al. have demonstrated in both adult and adolescent patients with PCOS that a fasting plasma glucose fails to identify a substantial portion of women who have IGT or DM2 by OGTT testing [46]. Similarly, recent evaluations of HbA1c for diagnosis of glucose intolerance in women with PCOS have proved disappointing. A study of 252 Turkish women with PCOS and 117 control women without PCOS [43] compared HbA1c levels with OGTT results and found that HgbA1c provided a less robust measure of testing with a 52.4% sensitivity, 74.4% specificity, 67.1% positive and 60.9% negative predictive values. Again, women who had IGT or DM2 by OGTT were misidentified as normal by HbA1c testing. Similarly, a retrospective study of 208 premenopausal women with PCOS [44] reported a poor sensitivity of 35% but excellent specificity of 99% using HbA1c = 6.5% for the diagnosis of diabetes in women with PCOS, compared with the diagnosis established by OGTT. The authors concluded that the HbA1c is less reliable than the OGTT to uncover glucose intolerance or diagnose diabetes in PCOS. In another study of 111 adult women with PCOS who were prospectively screened for DM2, IGT (pre-DM) and insulin resistance using various diagnostic methods and OGTT as the gold standard, screening with fasting plasma glucose failed to identify 41% of IGT and 20% of DM2 subjects. Further, OGTT and HbA1c had only fair agreement (κ = 0.29) [45].

Prevention of glucose intolerance in women with PCOS

Treatment options for reducing the rate of conversion to diabetes in women with PCOS focus on lifestyle modification, including the use of low glycemic index and low carbohydrate diets, and use of insulin sensitizing agents, specifically metformin. Use of thiazolidinediones had previously shown promise in this regard, but given recent concerns for risk for bladder cancer with prolonged pioglitazone use, caution with rosiglitazone and cardiac concerns, removal of troglitazone in the face of idiosyncratic hepatitis, and concern to bone health and increased fracture risk in postmenopausal women, this class of agents has fallen out of favor.

A recent systematic review [47] of six articles from five studies, with 137 women included, found subtle differences between various dietary interventions in PCOS. Greater weight loss was seen in monounsaturated fat-enriched diets, and low-glycemic index diets seemed to improve menstrual irregularity. Greater reductions in insulin resistance were seen with both low-carbohydrate and low-glycemic index diets. The authors found an improved quality of life with the use of a low-glycemic index diet and improved depression and self-esteem with a high-protein diet. Conversely, an undesirable increased in free androgen index resulted from high-carbohydrate diets, perhaps due to comparatively enhanced insulin release suppressing SHBG.

While several studies have demonstrated a reduction in progression to DM2 in non-PCOS individuals treated with the drug metformin, the only such study specifically in PCOS is a retrospective chart review of 50 women with PCOS, all of whom were started on metformin therapy at diagnosis, had OGTT testing at baseline, did not have diabetes at baseline and had a minimum of 1-year of follow-up with repeat OGTT testing. The study found that, at baseline, 39 women (78%) had NGT and 11 women (22%) had IGT. The women with NGT were followed for an average of 43.3 months and the women with IGT for 28.9 months. During these periods, the annual conversion rate from NGT or IGT to DM2 was 0% (none had developed diabetes), and 1.4% from NGT to IGT [48]. This rate of conversion from NGT to IGT was ˜10-fold lower than the conversion to IGT among women with PCOS with NGT not treated with metformin reported in the prospective studies mentioned above (16–19% NGT to IGT) [35,36].

Cardiovascular disease in PCOS Women with PCOS are often found to have an accumulation of risk factors for cardiovascular disease (CVD) including obesity, hypertension, low levels of HDL-c, elevated triglyceride levels, increased plasminogen activator inhibitor (PAI-1), increased endothelin-1, low levels of adiponectin and increased C-reactive protein levels. Anatomic and functional markers for CVD are also increased in women with PCOS, including increased carotid intima-medial thickness, coronary artery calcium (CAC) scores and abnormal flow mediated dilation, all suggesting an increased risk in women with PCOS.

In terms of lipids, in premenopausal women with PCOS, higher rates of dyslipidemia were found than in controls [49]. A case–control study of 195 non-Hispanic white women with PCOS [50] found elevations in LDL-c levels in women with PCOS, independent of obesity [50].

A prospective study followed 125 women with PCOS and 142 controls over the course of 3 years with B-mode ultrasonography of the carotid arteries to measure carotid intima-media wall thickness and plaque [51]. In those women aged 45 years or older, there was significantly more carotid mean intimal medial thickness in PCOS cases than in the control women, and this remained significant after adjusting for age and BMI [51]. In a study of 36 women with PCOS and 71 age- and BMI-matched control women aged 30–45 years (excluding those with diabetes and known coronary heart disease), evaluated by electron beam computed tomography to noninvasively measure CAC, 39% of women with PCOS compared with 21% of controls had CAC, and when compared with community dwelling women the prevalence was more startling still (9.9%; odds ratio, 5.9) [52]. An association was found between extent of coronary artery disease (CAD) on coronary angiography and presence of polycystic ovaries on ultrasound in 143 women <60 years old referred for assessment of chest pain or valvular disease in New Zealand in 1997, so that women with polycystic ovaries (42%) had more extensive coronary artery disease than women with normal ovaries (number of segments with >50% stenosis, 1.7 compared with 0.82). On logistic regression analysis of this data, the extent of coronary artery disease and family history of heart disease predicted the presence of polycystic ovaries [53].

Most notably, in a study, 30 young (mean age 22 years old) and lean (mean BMI 22 kg/m²) women with PCOS, without any prior known cardiovascular disease (CVD), were compared with 30 healthy age-and BMI-matched control women with flow-mediated dilation of the brachial artery and by Doppler ultrasound of the carotid arteries for intima-media thickness [54]. Compared with the normal control women, these young and lean women with PCOS were found to have impaired flow-mediated dilation, accompanied by an increased serum endothelin-1 level, and increased intima-media thickness of the carotid arteries. Hence, at an early age, these lean women with PCOS were already exhibiting anatomic and functional cardiac abnormalities placing them at risk for premature CVD.

Given the high prevalence of cardiovascular risk factors, it would not be surprising that women with PCOS would also have a higher prevalence of the metabolic syndrome (MBS). As background, the MBS in women is defined as having three out of five of the following criteria: waist circumference >35 inches (88 cm); triglyceride ≥150 mg/dl; HDL-c <50 mg/dl; blood pressure ≥130/85 mmHg; fasting plasma glucose ≥110 mg/dl. While MBS confers a two- to threefold higher risk for a cardiovascular event, the risk in women with MBS may be greater than that of men with MBS. Seven studies within a larger meta-analysis found that the risk of CV events and death is 30% higher in women than men meeting NCEP 2001 ATP III criteria for metabolic syndrome [55].

In a retrospective chart review of 106 women with PCOS, the prevalence of metabolic syndrome was 43%, nearly two- to threefold higher than that reported for age-matched women in the general population from NHANES III data, even when matched by BMI [56]. In this study, >90% of PCOS women had at least one of the five cardiovascular risk factors that comprise the MBS, and the most prevalent risk factor among the women was a low HDL-c. The higher prevalence of the MBS in women with PCOS is not confined to the USA, but has been confirmed in multiple studies conducted worldwide [57 –59].

Studies of cardiac outcomes in PCOS are limited in number, but overall support an increased risk of cardiovascular events. In the Nurses Health Study (NHS), which followed 82,439 women for 14 years, in women with very irregular periods the risk ratio for coronary heart disease was 1.5 and the risk ratio for fatal myocardial infarction (MI) was increased twofold [60]. Further epidemiological evidence of increased cardiovascular events in postmenopausal women with a history of PCOS (defined by irregular menses and elevated androgen measurements) was found in a subset of the NIH's National Heart, Lung, and Blood Institute (NHLBI) sponsored prospective Women's Ischemia Syndrome Evaluation (WISE) study. The cumulative 5-year cardiovascular event rate was 21.1% for women with clinical features of PCOS (n = 104) versus 11.3% for women without clinical features of PCOS (n = 286) [61].

Counter to these data is a retrospective review of death certificates in the UK from women with PCOS not showing a statistically significant increase in MI compared with the general population. However, this study was powered to detect a threefold increase in risk and only 786/1028 charts were analyzed, and while the standardized mortality ratio for ischemic heart disease was 1.4 for PCOS, this did not meet statistical significance [62].

Conversely and consistent with the results of the NHS and WISE studies, in a 20-year retrospective study of 2301 women with PCOS totalling >12,000 person-years, Mani et al. found that the prevalence of MI in the age group 45–54 was 1.9%, age 55–64 was 6.0% and >65 years 27.3%. Prevalence of angina age 45–54 was 2.6%, age 55–64 was 6.0% and > 65 years was 27.3%. Age-group-specific odds ratios for the prevalence of MI and angina compared with the local female population ranged between 2.6 and 12.9. The highest odds ratio was for MI in the group of women with PCOS >65 years old [63].

When considered collectively, the majority of data support the idea that women with PCOS, independently of adiposity, are at increased risk for atherosclerosis, and should be screened and targeted for primary prevention of CVD.

This is in line with guideline recommendations of the Androgen Excess and PCOS society [64].

Reproductive consequences in PCOS

Prevalence

PCOS affects 5–10% of women of childbearing age in the USA (3–5 million women), and is currently the leading cause of anovulatory infertility [65,66]. Anovulation presents clinically as irregular menstrual cycles (either amenorrhea or oligomenorrhea) and infertility. Seventy-five percent of women with PCOS have infertility due to anovulation. In addition, early (first trimester) miscarriages are threefold the rates of women without PCOS [67].

Weight loss of 5–10% can restore ovarian function and ovulation in approximately 50% of patients with PCOS and is thus an important pillar of fertility care in women with this disorder. It seems likely that this phenomenon is mediated via improved insulin sensitivity. However, sustained weight loss can be difficult to achieve which in turn results in the need for additional therapeutic strategies in many cases.

First-line medical strategies

The two most commonly used medical therapies to treat infertility in women with PCOS are clomiphene citrate and metformin. Clomiphene citrate acts as an anti-estrogen which displaces endogenous estrogen from the hypothalamic estrogen receptor and thus removes negative feedback by endogenous estrogens. Clomiphene acts as an indirect stimulator of FSH secretion. It restores ovulation in nearly 80% of women and results in an approximate 50% conception rate usually within three cycles of use. The primary adverse effect of clomiphene citrate is the increased rate of multiple gestations. Metformin is thought to treat infertility by improving insulin sensitivity. In a trial of 16 obese women with PCOS treated with metformin for 6 months and evaluated by the euglycemic-hyperinsulinemic clamp technique, glucose utilization and insulin action improved and was accompanied by significant increases in the levels of sex hormone-binding globulin and decreases in free testosterone and androstenedione levels [68]. Among these women, 44% resumed normal cycles and two cases of spontaneous pregnancy occurred during treatment. Current expert theory proposes that reducing levels of circulating insulin will decrease intra-ovarian concentrations of androgens and normalize gonadotropin secretory dynamics.

One study followed 61 obese women with PCOS, randomized to either metformin or placebo, for spontaneous ovulation over 35 days, and then administering clomiphene for 5 days to those women who did not ovulate (21 in metformin arm and 25 in placebo arm), while continuing either metformin or placebo, and then monitoring serum progesterone levels. The authors found that the women randomized to metformin receiving clomiphene had a significant reduction in mean AUC of insulin after oral glucose administration, whereas those on placebo did not, and 19 of 21 women on metformin + clomiphene ovulated (90%) versus 2 of 25 on placebo + clomiphene ovulated (8%) [69]. In another study of non-obese women with PCOS with normal OGTT, the rate of ovulation after initiation of metformin therapy demonstrated a graded increase over a 6 month time course with peak ovulation rate at months 5 and 6 of therapy [70]. In a head to head randomized controlled trial (RCT) of clomiphene citrate to metformin in non-obese anovulatory women with PCOS [71], 6 months of administration of metformin was more effective than six cycles of clomiphene citrate based on a non-statistically different ovulation rate between the two treatment groups (62.9 vs 67.0%), but with a significantly higher pregnancy rate in the metformin group (15.1 vs 7.2%), a lower rate of abortion with metformin therapy over 6 months (9.7 vs 37.5%), as well as a positive trend for live-birth rate favoring metformin therapy (83.9 vs 56.3%). The cumulative pregnancy rate was significantly higher in the metformin group than the clomiphene citrate group (68.9 vs 34.0%). Ovulation rates were higher initially with clomiphene citrate use in the first cycle but steadily rose with longer duration of metformin use over the course of 6 months to surpass rates with clomiphene citrate by month 6 (month 1: metformin 42% vs clomiphene 83%; in month 6: metformin 86% versus clomiphene 48%) [71]. In 2012, a systematic review and meta-analysis of four RCTs comparing metformin with clomiphene citrate in women with PCOS and BMI <32 kg/m² found no statistically significant difference for any outcome (ovulation, pregnancy, live birth, miscarriage and multiple pregnancy rates) between these two treatment modalities [72]. The authors did caution that there were conflicting findings and heterogeneity across the RCTs.

A meta-analysis of 13 RCTs including 428 women with PCOS found a 46% rate of ovulation in those PCOS women assigned to metformin monotherapy versus 24% in those receiving placebo [73]. Another such meta-analysis found that metformin was 50% better than placebo for ovulation induction in infertile PCOS patients, but was not of confirmed benefit versus placebo for achievement of pregnancy [74]. A subsequent meta-analysis in 2008 of 17 studies in 1639 women compared metformin versus placebo, and metformin + clomiphene versus clomiphene alone [75]. In the 10 trials comparing metformin monotherapy to placebo, metformin improved the odds of ovulation. There was a 1.56-fold increase in clinical pregnancy rate, but this was not statistically significant [75]. Metformin combined with clomiphene increased the likelihood of ovulation (and pregnancy), compared with clomiphene therapy alone [75]. A Cochrane meta-analysis of metformin monotherapy in PCOS found an improved ovulation rate in 16 RCTs with 1208 subjects. There was also an improved rate for clinical pregnancy with metformin use in eight RCTs in 707 subjects. In combination with clomiphene, metformin improved clinical pregnancy rates but this combination did not lead to improved live-birth rates. Metformin was also associated with a significantly higher incidence of gastrointestinal disturbances than placebo but no serious adverse effects were reported [76].

In 2007 the Pregnancy in Polycystic Ovary Syndrome study (PPCOS) randomized 626 infertile women with PCOS to clomiphene citrate plus placebo, extended-release metformin plus placebo, or a combination of metformin and clomiphene for up to 6 months. Adding metformin to clomiphene citrate increased the ovulation rate by 20%. In this study, the live-birth rate was 22.5% in the clomiphene group, 7.2% in the metformin group and 26.8% in the combination-therapy group, but the difference in live-birth rates between the clomiphene group and combination-therapy group did not attain statistical significance. Notably, multiparity was 6.0% in the clomiphene group, 0% in the metformin group and 3.1% in the combination-therapy group [77].

Because of the lack of a statistically significant difference in live-birth rates between clomiphene alone and clomiphene in combination with metformin in this study, the use of metformin for fertility induction has somewhat fallen out of favor and does not figure in the Endocrine Society's guidelines on PCOS [42]. However, it should be noted that in the PPCOS study patients were not allowed a run-in time of metformin therapy which may well have affected results. Since its publication – and not included in the Endocrine Society guideline – a 2012 study of 320 anovulatory women with PCOS randomized to metformin versus placebo found a 45% increase in live-birth rate after metformin use compared with placebo. Metformin significantly improved both pregnancy and live-birth rates over placebo (pregnancy rate: 53.6 vs 40.4%; live-birth rate: 41.9 vs 28.8%) [78]. Perhaps this discrepancy is due to methodological differences in study protocols by which the PPCOS study allowed insufficient time for sufficient improvement in insulin sensitivity with metformin therapy.

There are data suggesting that metformin use in PCOS may reduce the rate of early pregnancy loss. In a retrospective study of PCOS women treated for infertility in one clinic, rates of early pregnancy loss were lower (8.8%; 6 of 68 pregnancies) in the group treated with meformin, as compared with 41.9% (13 of 31 pregnancies) in the control group [79]. Subsequently in a prospective study of 208 pregnant women (98 women with PCOS treated with metformin throughout pregnancy and 110 normal pregnant controls), there was a reduction in miscarriage rate (9.1 vs 20%), gestational diabetes (0 vs 13%) and gestational hypertension (0 vs 11%) and a non-significant decrease in pre-eclampsia (0 vs 3%), in women with PCOS treated with metformin preconception to 37 weeks gestation [80].

Safety of metformin in pregnancy & lactation

Metformin is considered a Class B drug in pregnancy, meaning that metformin is not teratogenic when used in animal models of pregnancy. When compared with insulin for treatment of gestational diabetes (GDM), in 751 women with GDM randomized at 20–33 weeks gestation to either open-label metformin (supplemental insulin if required) or insulin, metformin was found to be safe. No serious adverse events were associated with metformin use [81]. In a prospective study of 126 live births (122 pregnancies) to 109 women with PCOS who conceived while on metformin and continued metformin through pregnancy, it was determined that metformin use reduced the prevalence of gestational diabetes, was not found to be teratogenic, and did not adversely affect birth length and weight, growth or motor-social development in the first 18 months of these babies' lives compared with controls [82]. An RCT of 257 pregnant women with PCOS randomized to metformin versus placebo from first trimester to delivery found no difference in pregnancy complications between arms in preeclampsia prevalence, GDM, or preterm delivery, or in a composite of those outcomes. Women in the metformin group gained less weight during pregnancy than those on placebo. There was no difference in fetal weight [83].

A prospective pharmacokinetic study of metformin concentrations in breast milk samples in six women found that the relative infant dose was <0.5% of the mother's weight adjusted dose, and the authors concluded that infant exposure to metformin through breast milk is low [84]. Similarly, another study in seven breastfeeding women taking metformin, concentrations of metformin were measured by high performance liquid chromatography and found that the mean relative infant dose was 0.28% (0.16–0.4%). Metformin was found in undetectable to very low plasma concentrations in the infants. No health concerns were noted in the infants evaluated [85].

In follow-up questionnaires regarding breast size increment and breastfeeding patterns, 1-year postpartum, from participants of a completed RCT [83] in which 240 participants with PCOS were randomized to treatment with metformin or placebo from the first trimester to delivery, no difference was found between the two groups. It was concluded that metformin had no impact on breastfeeding based on the 186 responders [86].

In conclusion, it is likely that metformin use in pregnancy and lactation is safe.

Individualized care

On an individual basis, the clinician must ultimately tailor fertility treatment to the patient's particular timeline. The onset of action of metformin will be slower than clomiphene citrate. It is critical to discuss with patients that clomiphene is a fertility drug that acts directly to induce ovulation with a rapid onset of action and that it is associated with significant multiparity [87]. In contrast, metformin affects metabolism to indirectly induce ovulation with a slow onset of action. It results in a more physiologic ovulation and release of a single egg at a time. An individual patient's favored timeline will help to direct therapy.

Alternative strategies

Letrozole is an aromatase inhibitor which induces ovulation without anti-estrogenic effects that can be seen with clomiphene. In clomiphene-resistant women with PCOS unable to achieve fertility, alternative strategies of adding metformin to clomiphene, versus using letrozole with and without additional metformin, versus bilateral ovarian drilling can be considered. In one RCT of 146 women with PCOS who did not conceive with clomiphene, there was no significant difference in ovulation (p = 0.24), pregnancy rate (p = 0.32) or abortion rate (p = 0.51) comparing those randomized to letrozole plus metformin versus bilateral ovarian drilling [88]. An RCT of letrozole compared with combined metformin and clomiphene citrate, in 250 women with PCOS who did not conceive on clomiphene alone, found no statistically significant difference either in ovulation frequency or in pregnancy rates (14.7 vs 14.4%) between these two arms [89]. Finally, a head to head combined metformin-letrozole versus metformin-clomiphene citrate trial in 59 women with PCOS who were clomiphene-resistant found no statistical difference in pregnancy rate in the metformin-letrozole group (10 patients, 34.5%) versus the metformin-clomiphene group (5 patients, 16.67%); however, there were more full term pregnancies with metformin-letrozole (10 patients, 34.5% vs 3 patients, 10%) [90]. The authors note that in this last study metformin was allowed a 6–8 week run-in period prior to additional agent use. As noted previously the pathophysiology of metformin affecting insulin resistance can take time.

Conclusion & future perspective

In summary, insulin resistance plays a critical role in both metabolism and reproduction of women with PCOS. Insulin resistance unifies the defects seen in PCOS of both increased risk for metabolic syndrome and anovulation and reproductive concerns. Future directions of research to tackle unresolved issues in PCOS care and understanding of underlying pathophysiologic mechanism may include pharmacogenetic evaluation of responders versus non-responders to metformin, the role of free fatty acid stimulation of androgens and the role that insulin plays, and whether there are ethnic/genetic differences in PCOS presentations. The molecular defect fundamentally underlying insulin resistance in PCOS has been hinted at by findings of post-receptor defects leading to abnormal patterns of phosphorylation of specific residues of the insulin receptor. The latter remains to be fully elucidated.

Financial & competing interests disclosure

The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.

No writing assistance was utilized in the production of this manuscript.

Executive summary

Evolution of a definition

Polycystic ovary syndrome (PCOS) is a clinical diagnosis.

PCOS can be present at any BMI, that is, in both thin and obese women.

When considering the diagnosis of PCOS, obtain tests to assess androgen status and exclude the following conditions: hyperprolactinemia, thyroid dysfunction, non-classical congenital adrenal hyperplasia and Cushing's syndrome if clinically indicated.

Cardiovascular disease in polycystic ovary syndrome

It is reasonable to consider all women with PCOS at risk of insulin resistance.

Clinical markers of insulin resistance in PCOS include obesity, increased waist-to-hip ratio, presence of acanthosis nigricans, low HDL-C, high triglycerides and low sex hormone-binding globulin.

Screening for women with PCOS should include a measure of adiposity (BMI, waist circumference), serial blood pressure measurements, serum lipid panel and evaluation for glucose intolerance using an oral glucose tolerance test. A fasting plasma glucose and HbA1c are not satisfactory screening tests for glucose intolerance in PCOS.

Consideration of dietary and lifestyle intervention and/or initiation of an insulin sensitizer (metformin) at the time of diagnosis of PCOS for primary prevention of DM2 and cardiovascular disease are recommended.

Reproductive consequence in polycystic ovary syndrome

The clinician musli:

– Assess the individual woman's sense of readiness or imperative for pregnancy at the time of presentation and diagnosis, or shortly thereafter.

– Recognize that:

Metformin may take a longer time to increase ovulation rates but may do so in a more physiologic fashion with less multiparity and less hyperstimulation syndrome

Clomiphene citrate may achieve swifter onset of increased ovulation in a pharmacologic fashion which may be more commonly associated with multiparity.

Alternative strategies for infertility are actively being explored.

References

Papers of special note have been highlighted as:

of interest; •• of considerable interest.

Stein

. Amenorrhea associated with bilateral polycystic ovaries. Am. J. Obstet. Gynecol. 29, 181–191 (1935).

Zawadzki

JKDA

. Diagnostic criteria for polycystic ovary syndrome: towards a rational approach. NIH Expert Conference on PCOS 1991, 377–384 (1992).

Along with [3] and [7], these references comprise the most frequently cited definitions for polycystic ovary syndrome (PCOS) and highlight the ongoing controversy surrounding PCOS to the present time.

The Rotterdam ESHRE/ASRM-Sponsored PCOS Consensus Workshop Group. Revised 2003 consensus on diagnostic criteria and long-term health risks related to polycystic ovary syndrome. Fertil. Steril. 81(1), 19–25 (2004).

Along with [2] and [7], these references comprise the most frequently cited definitions for PCOS and highlight the ongoing controversy surrounding PCOS to the present time.

Azziz

. Controversy in clinical endocrinology: diagnosis of polycystic ovarian syndrome: the Rotterdam criteria are premature. J. Clin. Endocrinol. Metab. 91(3), 781–785 (2006).

Franks

. Polycystic ovary syndrome. N. Engl. J. Med. 333(13), 853–861 (1995).

10.

Lowe

Kovacs

Howlett

. Incidence of polycystic ovaries and polycystic ovary syndrome amongst women in Melbourne, Australia. Aust. NZ J. Obstet. Gynaecol. 45(1), 17–19 (2005).

11.

Azziz

Carmina

Dewailly

. The Androgen Excess and PCOS Society criteria for the polycystic ovary syndrome: the complete task force report. Fertil. Steril. 91(2), 456–488 (2009).

12.

Along with [2] and [3], these references comprise the most frequently cited definitions for PCOS and highlight the ongoing controversy surrounding PCOS to the present time.

13.

Kahn

Flier

Bar

. The syndromes of insulin resistance and acanthosis nigricans. Insulin-receptor disorders in man. N. Engl. J. Med. 294(14), 739–745 (1976).

14.

Taylor

Dons

Hernandez

Roth

Gorden

. Insulin resistance associated with androgen excess in women with autoantibodies to the insulin receptor. Ann. Intern. Med. 97(6), 851–855 (1982).

15.

Burghen

Givens

Kitabchi

. Correlation of hyperandrogenism with hyperinsulinism in polycystic ovarian disease. J. Clin. Endocrinol. Metab. 50(1), 113–116 (1980).

16.

Nestler

Jakubowicz

De Vargas

Brik

Quintero

Medina

. Insulin stimulates testosterone biosynthesis by human thecal cells from women with polycystic ovary syndrome by activating its own receptor and using inositolglycan mediators as the signal transduction system. J. Clin. Endocrinol. Metab. 83(6), 2001–2005 (1998).

17.

Nestler

Jakubowicz

. Decreases in ovarian cytochrome P450c17 alpha activity and serum free testosterone after reduction of insulin secretion in polycystic ovary syndrome. N. Engl. J. Med. 335(9), 617–623 (1996).

18.

Nestler

Barlascini

Matt

. Suppression of serum insulin by diazoxide reduces serum testosterone levels in obese women with polycystic ovary syndrome. J. Clin. Endocrinol. Metab. 68(6), 1027–1032 (1989).

19.

Poretsky

Cataldo

Rosenwaks

Giudice

. The insulin-related ovarian regulatory system in health and disease. Endocr. Rev. 20(4), 535–582 (1999).

20.

Nandi

Chen

Patel

Poretsky

. Polycystic ovary syndrome. Endocrinol. Metab. Clin. North Am. 43(1), 123–147 (2014).

21.

Imperato-Mcginley

Peterson

Sturla

Dawood

Bar

. Primary amenorrhea associated with hirsutism, acanthosis nigricans, dermoid cysts of the ovaries and a new type of insulin resistance. Am. J. Med. 65(2), 389–395 (1978).

22.

Nagamani

Van Dinh

Kelver

. Hyperinsulinemia in hyperthecosis of the ovaries. Am. J. Obstet. Gynecol. 154(2), 384–389 (1986).

23.

Geffner

Kaplan

Bersch

Golde

Landaw

Chang

. Persistence of insulin resistance in polycystic ovarian disease after inhibition of ovarian steroid secretion. Fertil. Steril. 45(3), 327–333 (1986).

24.

Dunaif

Green

Futterweit

Dobrjansky

. Suppression of hyperandrogenism does not improve peripheral or hepatic insulin resistance in the polycystic ovary syndrome. J. Clin. Endocrinol. Metab. 70(3), 699–704 (1990).

25.

Richards

Cavallo

Meyer

3rd . Obesity, acanthosis nigricans, insulin resistance, and hyperandrogenemia: pediatric perspective and natural history. J. Pediatr. 107(6), 893–897 (1985).

26.

Plymate

Matej

Jones

Friedl

. Inhibition of sex hormone-binding globulin production in the human hepatoma (Hep G2) cell line by insulin and prolactin. J. Clin. Endocrinol. Metab. 67(3), 460–464 (1988).

27.

Nestler

Powers

Matt

. A direct effect of hyperinsulinemia on serum sex hormone-binding globulin levels in obese women with the polycystic ovary syndrome. J. Clin. Endocrinol. Metab. 72(1), 83–89 (1991).

28.

Dunaif

Graf

. Insulin administration alters gonadal steroid metabolism independent of changes in gonadotropin secretion in insulin-resistant women with the polycystic ovary syndrome. J. Clin. Invest. 83(1), 23–29 (1989).

29.

Smith

Ravnikar

Barbieri

. Androgen and insulin response to an oral glucose challenge in hyperandrogenic women. Fertil. Steril. 48(1), 72–77 (1987).

30.

Nestler

Singh

Matt

Clore

Blackard

. Suppression of serum insulin level by diazoxide does not alter serum testosterone or sex hormone-binding globulin levels in healthy, nonobese women. Am. J. Obstet. Gynecol. 163(4 Pt 1), 1243–1246 (1990).

31.

Conn

Jacobs

Conway

. The prevalence of polycystic ovaries in women with Type 2 diabetes mellitus. Clin. Endocrinol. (Oxf.) 52(1), 81–86 (2000).

32.

Peppard

Marfori

Iuorno

Nestler

. Prevalence of polycystic ovary syndrome among premenopausal women with Type 2 diabetes. Diabetes Care 24(6), 1050–1052 (2001).

33.

Escobar-Morreale

Roldan

Barrio

. High prevalence of the polycystic ovary syndrome and hirsutism in women with Type 1 diabetes mellitus. J. Clin. Endocrinol. Metab. 85(11), 4182–4187 (2000).

34.

Zachurzok

Deja

Gawlik

Drosdzol-Cop

Malecka-Tendera

. Hyperandrogenism in adolescent girls with Type 1 diabetes mellitus treated with intensive and continuous subcutaneous insulin therapy. Endokrynol. Pol. 64(2), 121–128 (2013).

35.

Miyoshi

Nagai

Takeda

. Ovarian morphology and prevalence of polycystic ovary syndrome in Japanese women with Type 1 diabetes mellitus. J. Diabetes Invest. 4(3), 326–329 (2013).

36.

Codner

Cassorla

. Puberty and ovarian function in girls with Type 1 diabetes mellitus. Horm. Res. 71(1), 12–21 (2009).

37.

Chang

Nakamura

Judd

Kaplan

. Insulin resistance in nonobese patients with polycystic ovarian disease. J. Clin. Endocrinol. Metab. 57(2), 356–359 (1983).

38.

Toprak

Yonem

Cakir

. Insulin resistance in nonobese patients with polycystic ovary syndrome. Horm. Res. 55(2), 65–70 (2001).

39.

Dunaif

Segal

Futterweit

Dobrjansky

. Profound peripheral insulin resistance, independent of obesity, in polycystic ovary syndrome. Diabetes 38(9), 1165–1174 (1989).

40.

Data supporting the premise that PCOS confers an increased risk of insulin resistance that is independent of BMI.

41.

Legro

Kunselman

Dodson

Dunaif

. Prevalence and predictors of risk for Type 2 diabetes mellitus and impaired glucose tolerance in polycystic ovary syndrome: a prospective, controlled study in 254 affected women. J. Clin. Endocrinol. Metab. 84(1), 165–169 (1999).

42.

Ehrmann

Barnes

Rosenfield

Cavaghan

Imperial

. Prevalence of impaired glucose tolerance and diabetes in women with polycystic ovary syndrome. Diabetes Care 22(1), 141–146 (1999).

43.

Solomon

Dunaif

. Long or highly irregular menstrual cycles as a marker for risk of Type 2 diabetes mellitus. JAMA 286(19), 2421–2426 (2001).

44.

Yildiz

Yarali

Oguz

Bayraktar

. Glucose intolerance, insulin resistance, and hyperandrogenemia in first degree relatives of women with polycystic ovary syndrome. J. Clin. Endocrinol. Metab. 88(5), 2031–2036 (2003).

45.

Norman

Masters

Hague

. Hyperinsulinemia is common in family members of women with polycystic ovary syndrome. Fertil. Steril. 66(6), 942–947 (1996).

46.

Ehrmann

Kasza

Azziz

Legro

Ghazzi

. Effects of race and family history of Type 2 diabetes on metabolic status of women with polycystic ovary syndrome. J. Clin. Endocrinol. Metab. 90(1), 66–71 (2005).

47.

Salley

Wickham

Cheang

Essah

Karjane

Nestler

. Glucose intolerance in polycystic ovary syndrome – a position statement of the Androgen Excess Society. J. Clin. Endocrinol. Metab. 92(12), 4546–4556 (2007).

48.

Legro

Arslanian

Ehrmann

. Diagnosis and treatment of polycystic ovary syndrome: an endocrine society clinical practice guideline. J. Clin. Endocrinol. Metab. 98(12), 4565–4592 (2013).

49.

Most recent formal guidelines for PCOS care endorsed by the Endocrine Society.

50.

Celik

Abali

Bastu

Tasdemir

Gul

. Assessment of impaired glucose tolerance prevalence with hemoglobin A(1)c and oral glucose tolerance test in 252 Turkish women with polycystic ovary syndrome: a prospective, controlled study. Hum. Reprod. 28(4), 1062–1068 (2013).

51.

Velling Magnussen

Mumm

Andersen

Glintborg

. Hemoglobin A1c as a tool for the diagnosis of Type 2 diabetes in 208 premenopausal women with polycystic ovary syndrome. Fertil. Steril. 96(5), 1275–1280 (2011).

52.

Hurd

Abdel-Rahman

Ismail

Abdellah

Schmotzer

Sood

. Comparison of diabetes mellitus and insulin resistance screening methods for women with polycystic ovary syndrome. Fertil. Steril. 96(4), 1043–1047 (2011).

53.

Legro

Finegood

Dunaif

. A fasting glucose to insulin ratio is a useful measure of insulin sensitivity in women with polycystic ovary syndrome. J. Clin. Endocrinol. Metab. 83(8), 2694–2698 (1998).

54.

Moran

Misso

. Dietary composition in the treatment of polycystic ovary syndrome: a systematic review to inform evidence-based guidelines. J. Acad. Nutr. Diet. 113(4), 520–545 (2013).

55.

Systematic review of dietary interventions in women with PCOS suggesting that low glycemic index and higher fat/lower carbohydrate diets may have some benefit over traditional low fat low calorie diets in women with PCOS.

56.

Sharma

Wickham

3rd Nestler

. Changes in glucose tolerance with metformin treatment in polycystic ovary syndrome: a retrospective analysis. Endocr. Pract. 13(4), 373–379 (2007).

57.

Talbott

Clerici

Berga

. Adverse lipid and coronary heart disease risk profiles in young women with polycystic ovary syndrome: results of a case–control study. J. Clin. Epidemiol. 51(5), 415–422 (1998).

58.

Legro

Kunselman

Dunaif

. Prevalence and predictors of dyslipidemia in women with polycystic ovary syndrome. Am. J. Med. 111(8), 607–613 (2001).

59.

Talbott

Guzick

Sutton-Tyrrell

. Evidence for association between polycystic ovary syndrome and premature carotid atherosclerosis in middle-aged women. Arterioscler. Thromb. Vasc. Biol. 20(11), 2414–2421 (2000).

60.

Christian

Dumesic

Behrenbeck

Oberg

Sheedy

2nd Fitzpatrick

. Prevalence and predictors of coronary artery calcification in women with polycystic ovary syndrome. J. Clin. Endocrinol. Metab. 88(6), 2562–2568 (2003).

61.

Birdsall

Farquhar

White

. Association between polycystic ovaries and extent of coronary artery disease in women having cardiac catheterization. Ann. Intern. Med. 126(1), 32–35 (1997).

62.

Orio

Jr. Palomba

Cascella

. Early impairment of endothelial structure and function in young normal-weight women with polycystic ovary syndrome. J. Clin. Endocrinol. Metab. 89(9), 4588–4593 (2004).

63.

Gami

Witt

Howard

. Metabolic syndrome and risk of incident cardiovascular events and death: a systematic review and meta-analysis of longitudinal studies. J. Am. Coll. Cardiol. 49(4), 403–414 (2007).

64.

Apridonidze

Essah

Iuorno

Nestler

. Prevalence and characteristics of the metabolic syndrome in women with polycystic ovary syndrome. J. Clin. Endocrinol. Metab. 90(4), 1929–1935 (2005).

65.

Thathapudi

Kodati

Erukkambattu

Katragadda

Addepally

Hasan

. Anthropometric and biochemical characteristics of polycystic ovarian syndrome in South Indian women using AES-2006 criteria. Int. J. Endocrinol. Metabol. 12(1), e12470 (2014).

66.

Orio

Vuolo

Palomba

Lombardi

Colao

. Metabolic and cardiovascular consequences of polycystic ovary syndrome. Minerva Ginecol. 60(1), 39–51 (2008).

67.

Chekir

Nakatsuka

Kamada

Noguchi

Sasaki

Hiramatsu

. Impaired uterine perfusion associated with metabolic disorders in women with polycystic ovary syndrome. Acta Obstet. Gynecol. Scand. 84(2), 189–195 (2005).

68.

Solomon

Dunaif

. Menstrual cycle irregularity and risk for future cardiovascular disease. J. Clin. Endocrinol. Metab. 87(5), 2013–2017 (2002).

69.

Shaw

Bairey Merz

Azziz

. Postmenopausal women with a history of irregular menses and elevated androgen measurements at high risk for worsening cardiovascular event-free survival: results from the National Institutes of Health – National Heart, Lung, and Blood Institute sponsored Women's Ischemia Syndrome Evaluation. J. Clin. Endocrinol. Metab. 93(4), 1276–1284 (2008).

70.

Pierpoint

Mckeigue

Isaacs

Wild

Jacobs

. Mortality of women with polycystic ovary syndrome at long-term follow-up. J. Clin. Epidemiol. 51(7), 581–586 (1998).

71.

Mani

Levy

Davies

. Diabetes and cardiovascular events in women with polycystic ovary syndrome: a 20-year retrospective cohort study. Clin. Endocrinol. (Oxf) 78(6), 926–934 (2013).

72.

Wild

Carmina

Diamanti-Kandarakis

. Assessment of cardiovascular risk and prevention of cardiovascular disease in women with the polycystic ovary syndrome: a consensus statement by the Androgen Excess and Polycystic Ovary Syndrome (AE-PCOS) Society. J. Clin. Endocrinol. Metab. 95(5), 2038–2049 (2010).

73.

Guideline by the Androgen Excess and PCOS Society regarding cardiovascular disease and PCOS.

74.

Knochenhauer

Key

Kahsar-Miller

Waggoner

Boots

Azziz

. Prevalence of the polycystic ovary syndrome in unselected black and white women of the southeastern United States: a prospective study. J. Clin. Endocrinol. Metab. 83(9), 3078–3082 (1998).

75.

Asuncion

Calvo

San Millan

Sancho

Avila

Escobar-Morreale

. A prospective study of the prevalence of the polycystic ovary syndrome in unselected Caucasian women from Spain. J. Clin. Endocrinol. Metab. 85(7), 2434–2438 (2000).

76.

Homburg

. The management of infertility associated with polycystic ovary syndrome. Reprod. Biol. Endocrinol. 1, 109 (2003).

77.

Diamanti-Kandarakis

Kouli

Tsianateli

Bergiele

. Therapeutic effects of metformin on insulin resistance and hyperandrogenism in polycystic ovary syndrome. Eur. J. Endocrinol. 138(3), 269–274 (1998).

78.

Nestler

Jakubowicz

Evans

Pasquali

. Effects of metformin on spontaneous and clomiphene-induced ovulation in the polycystic ovary syndrome. N. Engl. J. Med. 338(26), 1876–1880 (1998).

79.

Baillargeon

Jakubowicz

Iuorno

Jakubowicz

Nestler

. Effects of metformin and rosiglitazone, alone and in combination, in nonobese women with polycystic ovary syndrome and normal indices of insulin sensitivity Fertil. Steril. 82(4), 893–902 (2004).

80.

Palomba

Orio

Jr Falbo

. Prospective parallel randomized, double-blind, double-dummy controlled clinical trial comparing clomiphene citrate and metformin as the first-line treatment for ovulation induction in nonobese anovulatory women with polycystic ovary syndrome. J. Clin. Endocrinol. Metab. 90(7), 4068–4074 (2005).

81.

Misso

Costello

Garrubba

. Metformin versus clomiphene citrate for infertility in non-obese women with polycystic ovary syndrome: a systematic review and meta-analysis. Hum. Reprod. Update 19(1), 2–11 (2013).

82.

Lord

Flight

Norman

. Metformin in polycystic ovary syndrome: systematic review and meta-analysis. BMJ 327(7421), 951–953 (2003).

83.

Kashyap

Wells

Rosenwaks

. Insulin-sensitizing agents as primary therapy for patients with polycystic ovarian syndrome. Hum. Reprod. 19(11), 2474–2483 (2004).

84.

Creanga

Bradley

Mccormick

Witkop

. Use of metformin in polycystic ovary syndrome: a meta-analysis. Obstet. Gynecol. 111(4), 959–968 (2008).

85.

Tang

Lord

Norman

Yasmin

Balen

. Insulin-sensitising drugs (metformin, rosiglitazone, pioglitazone, D-chiro-inositol) for women with polycystic ovary syndrome, oligo amenorrhoea and subfertility. Cochrane Database Syst. Rev. 5, Cd003053 (2012).

86.

Legro

Barnhart

Schlaff

. Clomiphene, metformin, or both for infertility in the polycystic ovary syndrome. N. Engl. J. Med. 356(6), 551–566 (2007).

87.

Pregnancy in PCOS study comparing clomiphene versus metformin or combination therapy for infertility. There is some controversy regarding the interpretation of these findings and the methodology of metformin administration to consider.

88.

Morin-Papunen

Rantala

Unkila-Kallio

. Metformin improves pregnancy and live-birth rates in women with polycystic ovary syndrome (PCOS): a multicenter, double-blind, placebo-controlled randomized trial. J. Clin. Endocrinol. Metab. 97(5), 1492–1500 (2012).

89.

Study results published after the Endocrine Society clinical practice guidelines on PCOS, therefore not included.

90.

Jakubowicz

Iuorno

Jakubowicz

Roberts

Nestler

. Effects of metformin on early pregnancy loss in the polycystic ovary syndrome. J. Clin. Endocrinol. Metab. 87(2), 524–529 (2002).

91.

De Leo

Musacchio

Piomboni

Di Sabatino

Morgante

. The administration of metformin during pregnancy reduces polycystic ovary syndrome related gestational complications. Eur. J. Obstet. Gynecol. Reprod. Biol. 157(1), 63–66 (2011).

92.

Rowan

Hague

Gao

Battin

Moore

. Metformin versus insulin for the treatment of gestational diabetes. N. Engl. J. Med. 358(19), 2003–2015 (2008).

93.

Glueck

Goldenberg

Pranikoff

Loftspring

Sieve

Wang

. Height, weight, and motor-social development during the first 18 months of life in 126 infants born to 109 mothers with polycystic ovary syndrome who conceived on and continued metformin through pregnancy. Hum. Reprod. 19(6), 1323–1330 (2004).

94.

Vanky

Stridsklev

Heimstad

. Metformin versus placebo from first trimester to delivery in polycystic ovary syndrome: a randomized, controlled multicenter study J. Clin. Endocrinol. Metab. 95(12), E448–E455 (2010).

95.

Eyal

Easterling

Carr

. Pharmacokinetics of metformin during pregnancy. Drug Metab. Dispos. 38(5), 833–840 (2010).

96.

Hale

Kristensen

Hackett

Kohan

Ilett

. Transfer of metformin into human milk. Diabetologia 45(11), 1509–1514 (2002).

97.

Vanky

Nordskar

Leithe

Hjorth-Hansen

Martinussen

Carlsen

. Breast size increment during pregnancy and breastfeeding in mothers with polycystic ovary syndrome: a follow-up study of a randomised controlled trial on metformin versus placebo. BJOG 119(11), 1403–1409 (2012).

98.

Kulkarni

Jamieson

Jones

Jr . Fertility treatments and multiple births in the United States. N. Engl. J. Med. 369(23), 2218–2225 (2013).

99.

Abd Elgafor

. Efficacy of combined metformin-letrozole in comparison with bilateral ovarian drilling in clomiphene-resistant infertile women with polycystic ovarian syndrome. Arch. Gynecol. Obstet. 288(1), 119–123 (2013).

100.

Abu Hashim

Shokeir

Badawy

. Letrozole versus combined metformin and clomiphene citrate for ovulation induction in clomiphene-resistant women with polycystic ovary syndrome: a randomized controlled trial. Fertil. Steril. 94(4), 1405–1409 (2010).

101.

Sohrabvand

Ansari

Bagheri

. Efficacy of combined metformin-letrozole in comparison with metformin-clomiphene citrate in clomiphene-resistant infertile women with polycystic ovarian disease. Hum. Reprod. 21(6), 1432–1435 (2006).

Polycystic Ovary Syndrome and Insulin: Our Understanding in the Past,Present and Future

Abstract

Keywords

Evolution of a definition

Metabolic consequences of PCOS

Insulin resistance in PCOS

Role of insulin resistance in androgen excess in PCOS

Prevalence of insulin resistance in women with PCOS

Detection of glucose intolerance in women with PCOS

Prevention of glucose intolerance in women with PCOS

Reproductive consequences in PCOS

Prevalence

First-line medical strategies

Safety of metformin in pregnancy & lactation

Individualized care

Alternative strategies

Conclusion & future perspective

Financial & competing interests disclosure

References