Abstract
The risk of trisomy 21 increases with maternal age; however, serum screening is offered to women of all ages. It is unknown whether women in different age groups perceive their age-related risk of Down's syndrome differently. When Down's syndrome screening was initially introduced, the focus was on women over 35 years of age, which led to low detection rates of fetuses with Down's syndrome as this age group constitutes only approximately 10–13% of the pregnant population. There has been a tremendous input of resources into Down's syndrome screening and research has established screening methods with significant detection rates at lower false-positive rates. The reported uptake of screening tests is in the region of 80% in earlier studies [1]; however, trends in uptake over the years have not been studied nationally. A recent study from The Netherlands [2] showed the overall prenatal screening uptake rate to be 46% with individual uptake rates of 38 and 53% for serum screening and nuchal translucency (NT) measurement, respectively. A recent study from Hull and East Yorkshire [3] showed a significant decline in the uptake of second trimester serum screening (triple test-hCG, estriol and α-fetoprotein) over a 14-year period. During that period no first trimester screening was offered except by the private sector in the form of nuchal scans, and these women were very few and were identified and accounted for. This article follows up on our previous work on trends in uptake of serum screening [3], but with an examination of trends according to 5-year age cohorts over a 4-year period to try and determine which age group was responsible for the observed reduced uptake in screening.
The uptake of serum screening has been shown to depend on informed choice, which is poorly promoted by healthcare professionals in ethnic minority groups [4]. In this study the authors suggest that positive attitudes towards screening are more likely in the White population than in socially disadvantaged women. Of interest is that this finding is in contrast with our findings in a population where abortion is widely accepted and is largely (98%) Caucasian according to the 2001 census. The National Institute for Health and Clinical Excellence (NICE) has provided healthcare workers in England and Wales caring for pregnant women with a framework for screening for chromosomal abnormalities with the expected standards of performance of screening tests in their guideline on antenatal care for healthy women in the National Health Services (NHS).
Aims
We aimed to establish the screening acceptance trends according to 5-year age cohorts and assess whether there was an age bias in the decline in screening uptake.
Methods
Serum screening in this paper refers to the triple test (hCG, α-fetoprotein and serum estriol), which is routinely offered in the second trimester and it is the main form of Down's syndrome screening our unit has been offering since the screening program began in 1992. All women who were screened at an earlier stage in pregnancy were accounted for and excluded, and this was largely carried out in the private sector. The population of women in the Hull and East Yorkshire area of the UK who booked for antenatal care (20,970 women) between 2002 and 2007 was studied. All women were routinely offered serum screening for Down's syndrome with the triple test between 15 and 18 weeks’ gestation by one-to-one counseling with a midwife. All women were booked for delivery in one maternity unit and the clinical biochemistry laboratory analyzed all samples. Two unlinked databases were accessed: all deliveries by year from 2002 to 2007 and the clinical biochemistry laboratory database of all triple tests from the region as identified by the hospital in the same period. Databases available comprised all deliveries for the years 2002–2007 from Hull and East Yorkshire Women and Children's Hospital where all women in the area deliver. The total population studied was 20,970 women who were offered screening during the study period. The data from all sources has been recorded contemporaneously. This gives us confidence in our database as it was recorded and kept by a single laboratory that analyses all samples for all women screened in the Hull and East Yorkshire region. The following details were available: maternal date of birth, date of delivery, parity and gestation at delivery, and outcome of delivery. Using this data we were able to calculate the maternal age at the time of delivery, which was used to calculate maternal age at the time of screening for Down's syndrome. The number of women screened each year was obtained from a contemporary database from the Immunology and Biochemistry laboratory.
The private screening service data were accessed for the years 2003–2006. From these data we categorized screened women into same-age cohorts as described previously, namely: 19.9 and under, 20–24.9, 25–29.9, 30–34.9 and 35 years or older. These were then added to the number of women screened in hospital to obtain the total number of women screened each year in each age cohort. This private screening service only consisted of an early NT ultrasound scan. We must emphasize that the use of NT screening is not routinely offered in the NHS.
Results
Ages of women available for screening
The uptake rates of screening indicate that women in the age groups 25–29.9 and 30–34.9 who are at least 50% of all pregnant women have reduced their uptake of screening for Down's syndrome from 63.2 and 65.1% in 2003 to 38.6 and 39% in 2006, respectively. Women over 35 years of age have a consistently high uptake rate compared with other age cohorts. Those in the 19.9 years and under age group have the lowest uptake rate, which is also consistent through the years of the study. The age cohort 20–24.9 shows a smaller decline in uptake, which is comparable to that of those under 19.9 years. This suggests that less women in the low-risk category are accepting screening. The trend in the uptake of serum screening shown in Table 1 and Figure 1 is consistent with our previously published data [3] with a slight difference of total uptake in 2005 as the databases were interrogated in a different manner.
Serum screening uptake by age category per year.
Uptake of Down's syndrome screening by age group per year.
The women who accessed the private screening service were 3% (74), 6.4% (147), 7.2% (172) and 8.6% (182) for the years 2003–2006, respectively, for all age cohorts. This was especially done in the first trimester by NT. Approximately 62.7% of the private screens were in women over 35 years of age.
Parity of women available for screening
The proportion of women booking for antenatal care who were offered screening in each parity category (0, 1, 2, 3 and ≥4) was not different from year to year for the 5-year period. Parity does not appear to be a factor in the decline in screening uptake as it shows a uniform pattern from year to year (Table 2). There were no statistical tests used in the analysis of the results presented.
Parity of women at the time of the second trimester serum screening test.
Discussion
The uptake of screening for Down's syndrome, and any other condition screened for in pregnancy, should be an informed choice that the woman takes having been provided with full information on the condition screened for, including risks of the screening itself and further invasive tests. This is a minimum requirement if screening is offered according to the UK National Screening Committee recommendations. However, women have reasons for the uptake of prenatal screening, which may not be related to access, process or equity of service provision.
A sustained decline in the uptake of serum screening in our population has been documented. The acceptance or refusal of prenatal screening involves a complex decision-making process by patients resulting from an interplay of religion, ethnicity, age, parity, knowledge of condition screened for, acquaintance with another affected child (either their own offspring or someone else's), quality of counseling (one-to-one counseling and provision of information leaflets on the condition being screened for, meaning of screening results and the need for further testing and its risks), absence of language or communication barriers, patients’ own perception of risk, attitudes towards termination of pregnancy and previous obstetric experience [5]. Fear of pregnancy loss associated with invasive testing is also a factor. The availability of ultrasound screening for fetal aneuploidy has not been widely available in the UK, being offered only privately. Its impact on screening uptake is not clear.
The data presented show a decline in serum screening uptake in all age groups with a greater decline in the 25–29.9 and 30–34.9-year age groups from 63.2 and 65.1% in 2003 to 38.6 and 39% in 2006, respectively. The uptake in women under 20 years of age has consistently been less than 40%. The uptake in women greater or equal to 35 years has consistently been high compared with all other age groups. An Australian study also found that older women were more likely to take up prenatal diagnosis tests [6]. This suggests that the older, high-risk woman is more worried about her likelihood of having a chromosomally abnormal baby. Indeed previous guidance from the USA recommended that women with a singleton pregnancy who are over 35 years of age at delivery should be offered prenatal diagnosis other than screening [7]. The new guidelines have since changed and now recommend screening for all women.
Our results from 2006 fall in line with the age-related risk spectrum (i.e., there is a higher uptake of screening in the older women and a progressive reduction in women of decreasing age). The 2003 results indicate that the two age groups of highest uptake do not conform to the spectrum of age-related risk, a situation that was resolved by 2006. We think that the biggest contribution to the decline in screening uptake noted in Yorkshire is mainly due to the two age cohorts of 25–29.9 and 30–34.9 years who constitute the majority of pregnant women.
Knowledge of the condition that is being screened for is a vital aid to the decision to accept or refuse a screening test, with high uptake rates in patients with a good understanding of Down's syndrome. Knowledge is influenced by religion, parity, quality of English spoken and acquaintance with a child affected with the condition [8]. This data cannot be extrapolated to a homogeneous population such as that found in the Hull and East Yorkshire area that, according to the 2001 population census, has only 0.3% as the largest minorities (Indian and Chinese) compared with the 97.7 and 98.8% White population in Hull and East Yorkshire, respectively [3]. There is evidence to suggest that knowledge may reduce uptake rates where screening uptake is already high, but not when uptake is already low [9].
The number of women in each parity category did not differ greatly from year to year over the 5-year study period. It is unlikely that parity has an influence on the uptake of prenatal screening. There are no studies that have been done to assess the impact of parity or a woman's previous obstetric experience on uptake of screening. A study from Australia looked at the influence of parity on prenatal diagnosis testing. Increasing parity was associated with a significantly decreased likelihood of diagnostic testing [6]. This may suggest that a woman who has had several karyotypically normal children will perceive herself as low risk and therefore opt out of screening or diagnostic testing.
Half of the women being screened consider their participation as routine with no active decision-making on their part. Approximately 25% actively decide to have the tests [10]. A study from Leeds in the UK found Down's syndrome screening uptake to be low in women who would not have been offered a screening test by virtue of them being perceived to be low risk [8]. The uptake in older women (high-risk) was consistently high as seen in our study. The reasons may not be apparent, but we have demonstrated that acceptance of prenatal serum screening for Down's syndrome has consistently decreased over many years [3] and that uptake rates have declined for all age groups in our area of Yorkshire. Have women become more accepting of a child with Down's syndrome or is there a better understanding of risk by the women? If this trend were irreversible, prenatal screening services would need to be modified appropriately by allocating funding according to need.
Future perspective
Screening for Down's syndrome has advanced greatly since it became widely available in the UK in the early 1990s. The advances have centered mostly on improving the screening tests, which has now been achieved. Our previous work, which is linked to this study, has shown that screening uptake is declining in the population we serve. Indeed some studies from Europe have shown a similar trend. We feel that attention should now focus on women's views and attitudes towards Down's syndrome screening. Other regions in the UK will need to assess their uptake rate. These valuable data will lead to appropriate allocation of resources for cost-effective Down's syndrome screening.
Executive summary
There is evidence that serum screening (especially second trimester) uptake rates are not as high as when screening programs were started in the early 1990s with our area of Yorkshire showing a significant downward trend in uptake over a 14-year period.
The reasons for this pattern are not apparent. However we hypothesized that among other reasons, age may be a factor in screening uptake with older women (high risk of aneuploidy) taking up screening more than younger women.
We looked at a comprehensive database kept by our clinical biochemistry laboratory that performs all triple tests for the region and categorized women into 5-year age cohorts.
The age cohorts 25–29.9 and 30–34.9, who constitute at least 50% of all pregnant women, showed the most significant decline in screening uptake from 65 to approximately 40%. Future studies to determine reasons for this trend may need to focus on this group of women.
Women aged 35 years or older have an almost consistent screening uptake pattern.
Younger women less than 25 years have the least uptake of screening as they may generally consider themselves low risk for aneuploidy.
Parity did not appear to influence screening uptake in our study.
A survey asking women why they may or may not take up screening would be the best method to unravel this complex matter.
Footnotes
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.
The authors state that they have obtained appropriate institutional review board approval or have followed the principles outlined in the Declaration of Helsinki for all human or animal experimental investigations. In addition, for investigations involving human subjects, informed consent has been obtained from the participants involved.