Background: Miscarriages occur to excess in sibships with neural tube defects (NTDs) and among maternal versus paternal relatives in NTD families. Folic acid prevents most NTDs. Its potential to prevent miscarriages has been controversial.
Aim: We evaluated the relationship of maternal line and periconceptional folic acid with miscarriage.
Methods: First cousins in Irish families with NTDs were interviewed about pregnancy outcomes and the health of their offspring.
Results: Miscarriages were not more frequent among pregnancies of maternal versus paternal first cousins. Folic acid intake during early pregnancy significantly reduced the risk of miscarriage from 15.7 to 9.6%, for an adjusted odds ratio of 0.37 (95% confidence interval 0.19, 0.72, p = 0.005).
Conclusions: Folic acid during pregnancy was associated with a reduction of approximately 60% in miscarriages. Miscarriages are common-one in every eight pregnancies in this study. If incorporated into pre-pregnancy counseling, these results could have significant public health impact.