Polyhydramnios at Term in Gestational Diabetes: Should We Be Concerned?

Background/Objectives: Pregnancies complicated by idiopathic polyhydramnios are linked to a heightened risk of numerous maternal and perinatal complications. We aim to study the implications of polyhydramnios in term pregnancies complicated with gestational diabetes mellitus (GDM). Methods: A prospective cohort study including 340 GDM cases was conducted. An ultrasound scan was conducted at term between 37 and 40 weeks and amniotic fluid volume (AFV) was assessed by measuring the amniotic fluid index (AFI) and the single deepest pocket (SDP). Maternal demographics and obstetric and perinatal outcomes were evaluated after delivery. We performed comparisons between groups with normal AFV and polyhydramnios (AFI ≥ 24 cm or SDP ≥ 8 cm), and between groups with normal and increased AFV (AFI or SDP ≥ 75th centile). A multivariate logistic regression analysis was performed to study association between AVF measurements and adverse maternal and perinatal outcomes. Results: We found that women with GDM and polyhydramnios at term had a higher risk of maternal (54.3 vs. 27.5%, p < 0.001) and perinatal adverse outcomes (65.7% vs. 46.5%, p < 0.03). The increased AFV group showed a higher risk of fetal overgrowth (LGA: 21.4% vs. 8.2%, p < 0.001 and macrosomia: 19.8% vs. 5.4%, p < 0.001, respectively) and a lesser risk of delivering an SGA fetus (6.3% vs. 13.6%, respectively). Both AFI and SDP showed a significant correlation with newborn weight (r = 0.27; p < 0.001 and r = 0.28; p < 0.001, respectively) and newborn centile (r = 0.26; p < 0.001 and r = 0.26 for both). Subsequent to conducting a multivariate logistic regression analysis adjusted for pregestational BMI, nulliparity, and insulin treatment, both AFI and SDP were significantly associated with perinatal complications, but AFI showed a stronger association with fetal overgrowth (aOR 1.11; p = 0.004 for a LGA fetus and aOR 1.12; p = 0.002 for macrosomia) and with lower risk of delivering an SGA fetus (aOR 0.89; p = 0.009) or IUGR fetus (aOR 0.86; p = 0.03). ROC analysis showed a poor diagnostic performance of both AFI and SDP for identifying macrosomia (AUC 0.68 for AFI, and 0.65 for SDP). Conclusions: Detection of polyhydramnios at term, whether using AFI or SDP, identifies a subgroup of women with gestational diabetes with higher risks of obstetric and perinatal complications. Cases with increased AFV (AFI ≥ 18 cm or SDP ≥ 6.5 cm) are also associated with an increased risk of fetal overgrowth and may require more intensive monitoring for management and optimal delivery timing, with the aim of improve perinatal outcomes.