Correcting for ethnicity when defining large for gestational age infants in diabetic pregnancies

The large-for-gestational-age (LGA) infant, defined as > 90th birthweight percentile, is associated with mild disturbances of maternal glucose tolerance. In the UK the same birthweight percentile charts are used for all ethnic groups when assessing LGA infants. The influence of maternal hyperglycaemia on LGA infants of Asian (Indian Subcontinent) mothers in the UK is likely to be under-reported, as Asian birthweights tend to be lower than White/Europid birthweights. We assessed the number of LGA infants born consecutively to 21 Asian and 26 White/Europid mothers with gestational diabetes mellitus (GDM), delivered between 37 and 42 weeks gestation, and also in 34 Asian and 121 White/Europid mothers with a positive screening test for GDM but a normal 75 g oral glucose tolerance test (OGTT). Large-for-gestational-age infants were identified using both the standard UK percentile charts of the Medical Research Council and percentile charts constructed from 30,418 Asian and 162,477 White/Europid singleton births, delivered between 37 and 42 weeks gestation to non-diabetic mothers delivered in the North West Thames Region of England. The standard Medical Research Council percentile charts, compared with the ethnically derived charts, identified fewer LGA Asian (7/56 vs 15/56) but more White/Europid infants (33/147 vs 21/147). When correcting for ethnicity more Asian than White/Europid GDM mothers delivered LGA infants (9/21 vs 3/26, chi 2 = 4.76, p < 0.05). The maternal 2 h OGTT plasma glucose was a significant independent contributor to birthweight in the Asian (r2 = 0.319, p < 0.0005) but not the White/Europid infants, in whom gestational age and maternal height were significant independent contributors to birthweight (r2 = 0.158, p < 0.0001). We conclude that ethnic influences are important when defining LGA infants and that mild disturbances of maternal glycaemia have a greater influence on the birthweight of Asian than White/Europid infants.