Multiple pregnancy with a complete hydatidiform mole and a normal fetus is prone to severe obstetrical complications and malignant transformation after birth. Prognostic information is limited for this rare form of gestational trophoblastic disease.

This study aimed to determine obstetrical outcomes and the risk of gestational trophoblastic neoplasia in women with multiple pregnancy with complete hydatidiform mole and coexisting normal fetus, and to identify risk factors for poor obstetrical and oncological outcomes to improve patient information and management.

This was a retrospective national cohort study of 11,411 records from the French National Center for Trophoblastic Disease registered between January 2001 and January 2022.

Among 11,411 molar pregnancies, 141 involved histologically confirmed multiple pregnancy with complete hydatidiform mole and coexisting normal fetus. Roughly a quarter of women (23%; 33/141) decided to terminate pregnancy because of presumed poor prognosis or by choice. Among the 77% of women (108/141) who continued their pregnancy, 16% of pregnancies (17/108) were terminated because of maternal complications, and 37% (40/108) ended in spontaneous miscarriage before 24 weeks’ gestation. The median gestational age at delivery in the remaining 47% of pregnancies (51/108) was 32 weeks. The overall neonatal survival rate at day 8 was 36% (39/108; 95% confidence interval, 27–46) after excluding elective pregnancy terminations. Patients with free beta human chorionic gonadotropin levels <10 multiples of the median were significantly more likely to reach 24 weeks’ gestation compared with those with free beta human chorionic gonadotropin levels >10 multiples of the median (odds ratio, 7.0; 95% confidence interval, 1.3–36.5; P=.022). A lower free beta human chorionic gonadotropin level was also associated with better early neonatal survival (the median free beta human chorionic gonadotropin level was 9.4 multiples of the median in patients whose child was alive at day 8 vs 20.0 multiples of the median in those whose child was deceased; P=.02). The overall rate of gestational trophoblastic neoplasia after a multiple pregnancy with complete hydatidiform mole and a normal fetus was 26% (35/136; 95% confidence interval, 19–34). All 35 patients had low-risk International Federation of Gynecology and Obstetrics scores, and the cure rate was 100%. Termination of pregnancy on patient request was not associated with lower risk of gestational trophoblastic neoplasia. Maternal complications such as preeclampsia and postpartum hemorrhage were not associated with higher risk of gestational trophoblastic neoplasia, and neither were high human chorionic gonadotropin levels or newborn survival at day 8.

Multiple pregnancy with complete hydatidiform mole and coexisting fetus carries a high risk of obstetrical complications. In patients who continued their pregnancy, approximately one-third of neonates were alive at day 8, and roughly 1 in 4 patients developed gestational trophoblastic neoplasia. Therefore, the risk of malignant transformation appears to be higher compared with singleton complete moles. Low levels of free beta human chorionic gonadotropin may be indicative of better early neonatal survival, and this relationship warrants further study.