OBJECTIVE: The importance of maternal autoantibody levels in congenital heart block and elucidation of maternal factors that may reduce disease burden require further clarification. STUDY DESIGN: Pregnancies complicated by maternal anti-Ro antibodies from 2007 through 2011 were retrospectively reviewed. RESULTS: In all, 33 women were followed up throughout pregnancy. Semiquantitative maternal anti-La levels were significantly higher in pregnancies complicated by fetal heart block of any degree (median difference, 227.5; P = .04), but there was no difference in maternal anti-Ro levels. In all, 94% of fetuses maintained normal conduction when the mother was treated with hydroxychloroquine or daily prednisone therapy throughout pregnancy, compared to 59% in the untreated group (odds ratio, 0.1; P = .04). CONCLUSION: Pregnancies complicated by fetal heart block did not have higher levels of maternal anti-Ro antibodies. Maternal anti-La level may be a useful predictor of fetal heart block. Maternal treatment with either hydroxychloroquine or daily low-dose prednisone throughout pregnancy may provide a protective effect.