Aims: Elevated HbA1c in gestational diabetes mellitus (GDM) is associated with adverse pregnancy outcomes. Whether late HbA1c can inform the timing of delivery is unclear. We sought to investigate the association between third-trimester HbA1c and adverse pregnancy outcomes.
Methods: Data were retrospectively collected from GDM pregnancies managed at Campbelltown Hospital from January 2017 to December 2020. Maternal and neonatal outcomes were compared across three HbA1c groups (<5.0%, 5.0–5.4 %, >5.4%) using chi-square tests and multiple logistic regression, adjusting for pre-pregnancy BMI, gestation at delivery and GDM treatment.
Results: Overall 897 (32.1%) had a third trimester HbA1c: HbA1c<5.0% (12.6%), HbA1c 5.0-5.4 (48.7%) and HbA1c > 5.4% (38.0%). Groups were similar in mean (30.8±5.3 vs 30.9±5.2 vs 30.9±5.0 years) and gestation at HbA1c (36.5±1.5 vs 36.51.4 vs 36.6±1.3 weeks). Significant differences were observed mean booking BMI (29.9±8.2 vs 29.5±6.7 vs 31.9±7.2 kg/m2) and birthweight (3390±464.7 vs 3387±467.9 vs 3474±2120 g), insulin use (p=0.003), diet-only management (p=0.009), hypertensive disorders of pregnancy (p=0.019), pre-eclampsia (p=0.047) and SCN/NICU admissions (p=0.001). Unadjusted, higher HbA1c was associated with late preterm birth (OR=2.065, 95% CI: 1.085-3.933, p=0.027). After adjustment, higher HbA1c was associated with neonatal SCN/NICU admission (OR=1.502, 95% CI: 1.066-2.117, p=0.020). No other outcomes were significantly associated with a higher HbA1c.
Conclusions: Elevated third-trimester HbA1c was associated with pre-eclampsia, hypertensive disorders of pregnancy, SCN/NICU admissions and late-preterm births, but not with other adverse outcomes. The increase in risk was not substantial, suggesting that HbA1c may have limited utility in guiding the timing of delivery.