Is misoprostol a teratogen?

There have been a number of case reports (more than 90% of which are from Brazil) and one animal study that suggest that fetal exposure to misoprostol increases the risk of particular types of lower limb anomalies, central nervous system anomalies (particularly Möbius syndrome), and upper limb anomalies. Three case-control studies (all from Brazil) have also demonstrated a higher prevalence of anomalies in misoprostol-exposed infants. However, the absolute risk of fetal anomaly after misoprostol exposure appears quite low. Evidence gathered from population-based registries in Brazil indicates that the observed incidence of these anomalies does not appear to be high, even though gestational misoprostol exposure seems relatively frequent in the country.

Indeed, while the relative risk of malformations appears real, epidemiological studies indicate that the absolute risk (i.e., the number of cases) is low. The best available evidence suggests that misoprostol should be considered a “mini-teratogen” which is defined as a medication resulting in less than 10 malformations per 1,000 births. Although it is hard to define the risk associated with in utero misoprostol exposure because the overall rate of malformation is low, the available scientific evidence places this risk at approximately 1 malformation per 1,000 births exposed to misoprostol in utero. These risk estimates should to be clearly communicated.

However, it is also important to place these risks in context. If a woman is using misoprostol to terminate an early pregnancy the possible teratogenic effects are only applicable in cases in which 1) the pregnancy continues after the woman has used misoprostol and 2) the woman chooses to continue that pregnancy to term. Finally, as misoprostol is safer than many of the other abortion methods employed by women in legally restrictive settings and as carrying a pregnancy to also confers risk (particularly in low resource settings), the possible teratogenic effects of misoprostol use should be examined within the broader context of pregnancy risk.

Reference: Philip N, Shannon C, and Winikoff B. Misoprostol and teratogenicity: Reviewing the evidence–Report of a meeting. Robert H. Ebert Program on Critical Issues in Reproductive Health Publication Series. New York: Population Council, 2003.

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