Relationship between maternal glycaemia and birth weight in glucose-tolerant women from different ethnic groups in New Zealand

Aim: The aim of this study was to compare the population attributable fraction (PAF) for a large baby (≥ 4 kg) due to glycaemia, weight and smoking in glucose-tolerant women from different ethnic groups. Methods: A retrospective review of screening for gestational diabetes (GDM) and associated birth weight was undertaken in New Zealand European (n = 529), Maori (n = 540) and Pacific (n = 916) women. The proportion with a large baby was compared by 1-h post 50-g glucose challenge test tertile and maternal weight tertile. Results: Large babies were more common from Pacific and European than Maori women (24.3%, 18.8%, 8.9%, respectively; P < 0.001). Birth weight increased significantly with increasing glucose among Pacific women (P < 0.001) even after adjusting for maternal weight and other confounders. The risk of having a large baby was 2.56 (1.82-3.60)-fold greater in women in the highest maternal weight tertile (≥ 84 kg), with a significantly greater PAF in Pacific women (27.2%, 12.9%, 16.4%, respectively; P < 0.001). The odds ratio (OR) of having a large baby increased with even mildly elevated maternal 1-h glucose concentrations [OR for 5.6-6.2 mmol/l: 1.54 (1.11-2.14); for ≥ 6.3 mmol/l: 2.06 (1.50-2.82)], with no ethnic differences in PAF (11.1-11.8%, 16.7-18.7%, respectively). Smoking and being Maori were associated with smaller babies. Conclusions: Increased maternal weight and glycaemia are associated with a greater proportion of large babies among glucose-tolerant women. Growth of Pacific babies may be more sensitive to a higher maternal glucose when the mother is obese.