Aims: This study compared the third trimester HbA1c among women with Gestational Diabetes Mellitus (GDM) with and without adverse neonatal outcomes.
Methods: This was a retrospective chart review of GDM pregnancies diagnosed and managed at Campbelltown Hospital January 2015 – December 2016. Primary outcome measure was a composite including macrosomia (birthweight >4000g), neonatal hypoglycaemia, neonatal jaundice, hyaline membrane disease, hypoxic ischaemic encephalopathy, shoulder dystocia and neonatal death. HbA1c was sent routinely by the obstetric team at 35-36 weeks gestation and action taken if the HbA1c s ≥ 5.6%. Women with gestation <35 weeks were excluded from the analyses.
Results: Of the 1,612 women with GDM with birth ≥35 weeks, 652 were excluded (28 twins, 442 no HbA1c and/or 171 HbA1c collected <35 weeks gestation). Mean age was 30.7±5.9 years, body mass index (BMI) was 29.5±13.3 kg/m2 and 61.4% were of European descent. Mean HbA1c was 5.4±0.4%. 178 (18.5%) had an adverse composite outcome including 92 (9.6%) with macrosomia. Other complications were uncommon. Compared with other women, HbA1c was marginally higher among women with a composite outcome (5.5±0.5% vs 5.4±0.4% respectively p=0.046). While composite complication rates were not significantly higher among those with HbA1c ≥5.6% vs below (21.0% vs 17.0% p=0.124), among those with HbA1c ≥6.0% vs below complication rates were higher (25/92: 27.5% vs 153/871: 17.6% p=0.021). There were no significant differences in mode of delivery among those with and without complications with vaginal delivery among 53.1% vs 62.1% p=0.23 respectively.
Conclusions: The 35-36 week HbA1c was of marginal utility for identifying pregnancies complicated by a composite of neonatal adverse outcomes. While Hba1c≥6.0% is associated with such complications, it has low sensitivity (25/178 (14.0)%).