Hydatidiform mole and subsequent pregnancy outcome: a population-based cohort study

The objective of the study was to investigate whether a history of hydatidiform mole (HM) is associated with an increased risk of adverse outcomes in subsequent pregnancies.

This was a nationwide cohort study with data from population-based registers. The study population consisted of all children registered in the Swedish Medical Birth Register 1973-2009 (n = 3,730,825). Odds ratios (ORs) with 95% confidence intervals (CIs) were estimated for adverse maternal and offspring pregnancy outcomes by maternal history of HM prior to the delivery, with children to women with no maternal history of HM as the reference. Risk estimates were adjusted for maternal age at delivery and maternal country of birth.

A history of HM was not associated with an increased risk of adverse maternal outcomes in subsequent pregnancies (n = 5186). Women exposed to a molar pregnancy prior to the index birth were at an almost 25% increased risk of preterm birth (OR, 1.23; 95% CI, 1.06-1.43), whereas women with at least 1 birth between the HM and the index birth were at an increased risk of a large-for-gestational-age birth and stillbirth (OR, 1.35; 95% CI, 1.10-1.67 and OR, 1.81; 95% CI, 1.11-2.96, respectively). The risk of repeat mole was 0.4%.

Women with a history of HM are at no increased risk of adverse maternal outcomes in subsequent pregnancies but have an increased risk of large-for-gestational-age birth, stillbirth, and preterm birth. However, in absolute terms, the risk of subsequent adverse offspring outcomes is very low.