Association Between Interpregnancy Interval and Adverse Birth Outcomes in Women With a Previous Stillbirth: An International Cohort Study

Interpregnancy interval (IPI; the length of time between pregnancies) is a risk factor for adverse outcomes in infants and their mothers. TheWorld Health Organization recommends women wait at least 2 years after a live birth and 6 months after miscarriage or abortion before conceiving again, but there is no recommendation for the best IPI after stillbirth. Other studies suggest that gestation length and an interval less than 6 months represent risk to maternal health status and adverse birth outcomes for the infant, respectively, so there is evidence to suggest that the optimal time after stillbirth is somewhere between 6 months and 2 years. The researchers sought to investigate the association between IPI after stillbirth and birth outcomes in the subsequent pregnancy. The researchers performed an international cohort study using data from birth records from Finland (1987-2016), Norway (1980-2015), andWestern Australia (1980-2015). Consecutive singleton pregnancies in women whose most recent pregnancy concluded in stillbirth of at least 22 weeks' gestation were included. Odds ratios (ORs) for stillbirth, preterm birth (PTB), and small-for-gestational-age (SGA) birth by IPI by country, adjusted for maternal age, parity, decade of delivery, and gestational length of the previous pregnancy, were calculated, with a fixed-effects meta-analysis used to estimate pooled ORs. Overall, 14,452 births in women with a stillbirth in the previous pregnancy were identified; median IPI after stillbirth was 9 months (interquartile range, 4-19 months). In this sample, 9109 women (63%) conceived within 12 months of stillbirth; of the 14,452 births, 228 (2%) were stillbirths, 2532 (18%) were PTBs, and 1284 (9%) were SGA births. Comparing to an IPI of 24 to 59 months, intervals shorter than 12 months were not associated with increased odds of subsequent stillbirth (pooled adjusted OR, 1.09 [95% confidence interval, 0.63-1.91] for <6 months; 0.90 [0.47-1.71] for 6-11 months), PTB (0.91 [0.75-1.11] for <6 months; 0.91 [0.74-1.11] for 6-11 months), or SGA birth (0.66 [0.51-0.85] for <6 months; 0.64 [0.48-0.84] for 6-11 months). In this study, the findings suggested that conception of another child within 1 year of stillbirth was not associated with increased risk of subsequent stillbirth, PTB, or SGA birth. The researchers note that short IPIs were more common after stillbirth than after live birth. Because 37% of women in this cohort became pregnant within 6 months of a stillbirth and 63% within 12 months, these results are applicable to a large pool of women conceiving after stillbirth. They recommend their study be replicated in a larger sample of women to investigate the risk of IPI and its relationship to recurrent stillbirth.