Aim: To re-examine the relationships between birth weight and maternal glycated haemoglobin (HbAlc) concentration at different time points in pregnancies complicated by pre-gestational type 1 diabetes.
Methods: A dataset was collected prospectively on all deliveries in Scotland to women with pre-gestational type 1 diabetes occurring during two 12 month periods (01/04/98 to 31/03/99 and 01/04/03 to 31/03/04). Relationships between standardised measures of birth weight and HbAlc at each time point were examined using correlation analysis.
Results: Standardised birth weights (Z scores) were calculated for 338 singleton live born infants. HbA1c concentrations were available for: 204 women (pre-pregnancy), 297 women (1st trimester), 314 women (2nd trimester) and 303 women (3rd trimester). Standardised birth weight showed a unimodal distribution shifted to the right relative to a reference population (Mean, +1.62 S.D). There was a significant negative correlation between pre-pregnancy HbAlc and birth weight (Spearman's Rho -0.138; p=0.049).
Conclusions: Standardised birth weights of the infants of diabetic mothers are higher than those of a reference population. There is no simple relationship between maternal glycaemic control and birth weight, but the previously described paradoxical inverse relationship between pre-pregnancy glycaemic control and birth weight has been confirmed using a larger dataset.