In New Zealand the rise in gestational diabetes mellitus (GDM) prevalence reflects the current patterns of increasing obesity and diabetes. Approximately 61,000 women give birth in New Zealand every year, and about 4.9% (6.6%) of those women have diabetes. Screening for gestational diabetes is recommended for all pregnant women in New Zealand, unless an earlier diagnosis of diabetes was made. Indigenous Maori women, Pacific Island, and Asian Indian women are populations genetically prone to diabetes, and have high rates of gestational and type 2 diabetes. Exposure of the foetus to maternal diabetes influences changes in birthweight, adiposity, and foetal insulin production. GDM and type 2 diabetes in Pacific Island and Maori new-borns were associated with higher birthweight, skinfold thicknesses, raised cord insulin, insulin peptides, and increased leptin concentrations. Pacific Island and indigenous Maori women gave birth to macrosomic new-borns, who commonly suffered postnatal hypoglycaemia, respiratory distress, and shoulder dystocia. The association between maternal obesity and SGA raises a concern as SGA is less likely to be detected in early pregnancy in obese women, while the association between SGA and socioeconomic status, initially observed in Maori and Pacific women, was explained by high cigarette smoking rates, and obesity in deprived areas.