How long after a miscarriage should women wait before becoming pregnant again? Multivariate analysis of cohort data from Matlab, Bangladesh

OBJECTIVE: To determine the optimum interpregnancy interval (IPI) following a miscarriage. DESIGN: Multivariate analysis of population-based, prospective data from a demographic surveillance system. SETTING: Pregnancies in Matlab, Bangladesh, between 1977 and 2008. PARTICIPANTS: 9214 women with 10 453 pregnancies that ended in a miscarriage and were followed by another pregnancy outcome. MAIN OUTCOME MEASURES: Outcome of pregnancy following the miscarriage was singleton live birth, stillbirth, miscarriage or induced abortion. For pregnancies that ended in live birth: early neonatal, late neonatal and postneonatal mortality. RESULTS: Compared with IPIs of 6–12 months, pregnancies that were conceived ≤3 months after a miscarriage were more likely to result in a live birth and less likely to result in a miscarriage (adjusted relative risk ratio (RRR) 0.70, 95% CI 0.57 to 0.86) or induced abortion (0.50, 0.29 to 0.89). Induced abortions were significantly more likely following IPIs of 18–24 months (2.36, 1.48 to 3.76), 36–48 months (2.73, 1.50 to 4.94), and >48 months (3.32, 1.68 to 2.95), and miscarriages were more likely following IPIs of 12–17 months (1.25, 1.01 to 1.56) and >48 months (1.90, 1.40 to 2.58). No significant effects of IPI duration are seen on the risks of a stillbirth. However, IPIs≤3 months following a miscarriage are associated with significantly higher late neonatal mortality for the infant born at the end of the IPI (adjusted hazard ratio (HR) 1.74, 1.06 to 2.84), and IPIs of 12–18 months are associated with a significantly lower unadjusted risk of postneonatal mortality (0.54, 0.30 to 0.96). CONCLUSIONS: The shorter the IPI following a miscarriage, the more likely the subsequent pregnancy is to result in a live birth. However, very short IPIs may not be advisable following miscarriages in poor countries like Bangladesh because they are associated with a higher risk of mortality for the infants born after them.