Breast‐feeding During Pregnancy and the Risk of Miscarriage

ContextBreastfeeding rates and durations have been increasing among American women in recent decades, but a consequence of these trends is that women may be more likely to practice breastfeeding during pregnancy (BDP). BDP has been hypothesized to increase the risk of miscarriage, yet there has been little research investigating if this is the case.MethodsUsing data on 10,661 pregnancies from the National Survey of Family Growth spanning 2002-2015, unadjusted miscarriage rates were calculated according to BDP status. Multivariate Cox proportional hazards models were used to investigate the association between BDP and the risk of miscarriage.ResultsBDP was practiced in 6.1% of the total time at risk of miscarriage. The miscarriage rate was elevated when mothers exclusively BDP (98.4 per 1000 person-months at risk) compared to when mothers were either complementary BDP or not breastfeeding. After adjusting for maternal and pregnancy characteristics, there was a nearly four-fold increase in the risk of miscarriage when mothers practiced exclusive BDP versus not breastfeeding and no increased risk associated with complementary BDP. The magnitude of the increase during exclusive BDP was similar to that of women who conceived above age 40, a well-known predictor of pregnancy loss.ConclusionExclusive BDP is associated with a heightened risk of miscarriage, but it remains unclear how the practice is associated with outcomes of the mother and breastfed child. More research is therefore needed to understand all of these potential relationships before any firm recommendations on the safety of the practice should be made.