Birthweight of Babies Born to Mothers with Type 1 Diabetes: is it Related to Blood Glucose Control in the First Trimester?

A retrospective study of 133 pregnancies in women with Type 1 diabetes was performed, and the 116 which progressed beyond 28 weeks were further analysed. Despite good maternal blood glucose control (mean (+/- SE) HbA1 levels 8.6 +/- 0.2% at the end of the first trimester; 6.9 +/- 0.2% at delivery; normal range 4.0-8.5%), 38% of babies had birthweights above the 90th centile and operative intervention occurred in 77 deliveries (66%). There was no significant correlation between birthweight and HbA1 level at any stage of pregnancy, but mothers with babies above the 90th centile for weight had a higher HbA1 at the end of the first trimester than mothers with babies below the 90th centile (9.3 +/- 0.5 vs 7.9 +/- 0.2%, p less than 0.05). In contrast there was no difference in the HbA1 levels at delivery (7.0 +/- 0.3 vs 6.8 +/- 0.2%). The perinatal mortality rate was 17.7 per 1000 births. The results confirm that in Type 1 diabetes large babies are common despite good blood glucose control, and suggest that maternal blood glucose control in the first trimester may be an important determinant of birthweight.