Pregnancy following Miscarriage: What is the Optimum Interpregnancy Interval?

“Each case should be assessed individually and advice regarding birth spacing should be tailored, taking into consideration maternal age, fertility behavior, socioeconomic status and comorbidities.”

Miscarriage, or the spontaneous loss of pregnancy at a relatively early stage of development, affects one in 20 pregnancies. For couples hoping to start a family, loss of a first pregnancy can be a devastating experience. Trying to come to terms with their grief, and to compensate for their loss, one of the questions foremost in their mind is ‘how long should we wait before trying for another pregnancy?’

“This study, although with several limitations, formed the sole basis of the WHO consultative group's recommendation of delaying pregnancy for at least 6 months following a miscarriage.”

In 2005, the WHO published a report of a technical consultation on birth spacing that reviewed the evidence surrounding the ideal birth interval following different types of pregnancy outcomes [101]. Although there was ample evidence from different populations to suggest that having a short birth interval following a live birth was detrimental for the next pregnancy, the evidence was scant regarding birth spacing after a miscarriage. Based on a single large-scale study conducted in Latin America, the consultative group recommended that couples wait for at least 6 months before trying to conceive after a miscarriage and called for more research in diverse populations. The evidence is still thin on the ground 5 years after the publication of the report.

Review of the evidence

An updated search of the literature using the search terms ‘miscarriage’, ‘birth spacing’ and ‘interpregnancy interval’ individually and in combination yielded six relevant published reports, including the Latin American study by Conde-Agudelo et al. used by the WHO technical consultative group [1]. However, there was good evidence to support delaying pregnancy after a term or preterm live or stillbirth. Conde-Agudelo's meta-analysis of 67 studies demonstrated that birth intervals of less than 18 months or greater than 59 months following live birth were associated with adverse maternal and perinatal outcomes in the next pregnancy [2]. With regard to pregnancies following miscarriage, the results from the few published studies give conflicting evidence. The oldest published article in this subject area was by Wyss et al., who did not find any statistically significant difference in the occurrence of preterm deliveries following miscarriage with birth intervals of less than 90 days in comparison with intervals greater than 90 days [3]. Basso et al. reported that the risk of adverse pregnancy outcomes such as preterm delivery, low birthweight and growth restriction actually increased with increasing interpregnancy intervals following miscarriage [4]. This was a population-based study using the Danish birth registry of 45,449 records of women who had had a previous miscarriage. Another study by Goldstein et al. from the USA did not find any association between birth intervals of less than 100 days following miscarriage and adverse outcomes such as preterm birth, low birthweight or perinatal deaths in the next pregnancy [5]. The large-scale Latin American study by Conde-Agudelo et al. referred to earlier used data collected from hospital admissions in the Perinatal Information System Database located in Uruguay [1]. They found that compared with interpregnancy intervals of 18–23 months, intervals of less than 6 months following abortions (both spontaneous and induced) were associated with adverse maternal and perinatal outcomes in the next pregnancy. This study, although with several limitations, formed the sole basis of the WHO consultative group's recommendation of delaying pregnancy for at least 6 months following a miscarriage. By the authors’ own admission, this study had several limitations. Perhaps the most important of these was its inability to distinguish between spontaneous miscarriage and induced abortion. The authors hypothesized that the possible explanation of their findings could lie in the increased rates of infection following induced abortion. Moreover, the data analyzed were from hospital admissions where diagnoses were not standardized or validated and the results were neither population based nor generalizable to a wider group. Around the same time, DaVanzo et al. published a report looking at the effects of interpregnancy intervals using data from a demographic surveillance system in Matlab, Bangladesh [6]. They found that interpregnancy intervals of 15–75 months were associated with a reduced chance of fetal loss in the next pregnancy independent of how the previous pregnancy ended. This also meant that if the previous pregnancy ended in a miscarriage, there was a higher risk of the subsequent pregnancy ending in another miscarriage, irrespective of the interpregnancy interval. This study had several strengths: large-scale population-based prospectively collected data, standardized diagnoses and coding criteria as well as controlling for several potential confounding factors. However, the findings were difficult to interpret as the reference group used in calculating the odds ratio was women who had a previous live birth and an interpregnancy interval of 27–50 months – and women who had a previous live birth are known to be at a lower risk of subsequent pregnancy loss than those whose previous pregnancy ended in miscarriage. Love et al. addressed this shortcoming by assessing second pregnancy outcomes in all Scottish women recorded to have had an initial miscarriage and found that best outcomes in the second pregnancy were associated with interpregnancy intervals of less than 6 months [7]. However, this report did not include miscarriages that did not warrant hospital admissions and could not distinguish between voluntary contraceptive use and involuntary subfertility when assessing the interpregnancy interval.

“…there remains little doubt that delaying pregnancy after a miscarriage is of little benefit and may indeed be detrimental to the health of the subsequent child.”

If we now look at the evidence presented objectively, there remains little doubt that delaying pregnancy after a miscarriage is of little benefit and may indeed be detrimental to the health of the subsequent child. In fact, this was evident at the time of writing of the report by the WHO consultative group on birth spacing. Only one study disputed this [1]; but the WHO consultative group felt that despite its limitations, the findings from such a large-scale study could not be ignored. There were also, one suspects, policy constraints underlying the recommendation. There is huge political pressure in developing countries such as India and China to streamline family size and increasing interpregnancy intervals by using modern contraceptive methods can only benefit family planning. There is also the problem of distinguishing between late miscarriage and preterm births in countries where gestational age is determined by maternal recall of her last menstrual period in the absence of routine ultrasound dating scans. Furthermore, the effect of maternal nutritional status and access to healthcare are quite different in the rest of the world compared with the west. Therefore, one can see the rationale behind the WHO's recommendation to delay the next pregnancy by at least 6 months following a miscarriage. From the point of view of the couple trying to conceive after a miscarriage, irrespective of the part of the world they live in, the WHO recommendations mean little or nothing – there is no ‘one-size-fits-all’ solution. Each case should be assessed individually and advice regarding birth spacing should be tailored, taking into consideration maternal age, fertility behavior, socioeconomic status and comorbidities. In fact, as many practitioners already advise, there is no evidence to suggest that delaying pregnancy following an uncomplicated miscarriage is beneficial for the next pregnancy. Couples should try for another pregnancy once they feel physically and mentally ready for it.

Acknowledgements

The authors would like to thank Eleanor Love for carrying out the initial literature search for this article.