BACKGROUND: Antenatal therapy with high-dose intravenous immunoglobulin (IVIG) may prevent gestational alloimmune liver disease (GALD). OBJECTIVE: The objective of this study was to determine the effectiveness of this approach in a large cohort of women at risk for poor pregnancy outcome due to GALD. METHODS: Women with a history of affected offspring were provided antenatal IVIG treatment and data were acquired prospectively from 1997 to 2015. The outcomes of treated pregnancies were compared to those of untreated pregnancies, and the effectiveness of starting at 14 weeks was compared to that of starting at 18 weeks. RESULTS: A total of 188 treated pregnancies in 151 women were analyzed. Only 30% (n = 105) of untreated gestations resulted in healthy offspring as compared to 94% (n = 177) of treated pregnancies (p < 0.0001). Treated gestations of both the 14-week (n = 108) and the 18-week (n = 80) start cohort showed a decreased rate of fetal loss relative to untreated gestations (p < 0.0001). Equivalent outcomes were recorded in the 18-week versus the 14-week start cohort (p > 0.05). Few adverse events or complications of antenatal therapy were recorded. CONCLUSION: Antenatal therapy with high-dose IVIG initiated at either 18 or 14 gestational weeks effectively prevents poor outcome of pregnancies at risk for GALD.