Breast-feeding During Pregnancy and the Risk of Miscarriage

CONTEXT Breast-feeding rates and durations have been increasing among U.S. women in recent decades. As a result, women may be more likely to practice breast-feeding during pregnancy (BDP), which has been hypothesized to increase the risk of miscarriage, yet there has been little research into the issue. METHODS Data on 10,661 pregnancies from several waves of the National Survey of Family Growth, covering the years 2002-2015, were used to calculate unadjusted miscarriage rates according to BDP status. Multivariate Cox proportional hazards models were employed to investigate the association between BDP and the risk of miscarriage. RESULTS BDP was practiced for 6% of the total time at risk of miscarriage. The miscarriage rate was higher when mothers exclusively breast-fed during pregnancy (35%) than when they practiced either complementary BDP (i.e., the child also consumed other food) or did not breast-feed (14% and 15%, respectively). After adjustment for maternal and pregnancy characteristics, the risk of miscarriage was greater when mothers exclusively breast-fed than when mothers did not breast-feed (hazard ratio, 3.9), but no increased risk was found with complementary BDP. The miscarriage risk during exclusive BDP was similar to that for women who conceived when they were 40 or older (3.2). CONCLUSIONS Exclusive BDP is associated with an elevated risk of miscarriage, but it remains unclear whether and how the practice is associated with health outcomes for the mother and breast-fed child. Research is needed to further explore these outcomes to inform recommendations regarding BDP.