Background
Rates of pre‐gestational obesity and gestational diabetes mellitus (GDM) are increasing in Australia. While both are established risk factors for neonatal hypoglycaemia, the additive effect of both risks on neonatal hypoglycaemia is not well understood.

Aims
To determine the influence of obesity on neonatal hypoglycaemia among infants born to GDM mothers. The authors hypothesise the presence of a greater frequency and severity of neonatal hypoglycaemia in infants born to obese GDM women.

Materials and methods
A cohort of 471 singleton GDM pregnancies was retrospectively studied. Women were divided into obese (body mass index (BMI) ≥ 30 kg/m2) and not‐obese (BMI < 30 kg/m2) groups according to self‐reported pre‐pregnancy weight. Perinatal outcomes and details of hypoglycaemic episodes were obtained by reviewing medical records. Results Twenty‐five percent (104/410) of the GDM mothers were obese, while 36% (146/410) exceeded pregnancy weight gain recommendations. GDM and obesity resulted in a greater frequency of neonatal hypoglycaemia as compared to women with GDM alone (obese 44%, not obese 34%, P = 0.046). Obesity increased the likelihood of having multiple hypoglycaemic episodes (P = 0.022). Excess weight gain increased the likelihood of the neonate requiring intravenous dextrose (P = 0.0012). No differences were found in the likelihood of nursery admissions or lowest plasma glucose levels. Conclusions Pre‐pregnancy obesity and weight gain during pregnancy above the recommended limits increased the likelihood of neonatal hypoglycaemia among infants of GDM mothers. Further studies with larger cohorts are warranted to confirm our findings.