Glycaemic control during early pregnancy and fetal malformations in women with Type I diabetes mellitus

Aims/hypothesis. To assess the relation between glycaemic control in early pregnancy and the risk of congenital malformations in offspring of mothers with Type I (insulin-dependent) diabetes mellitus. Methods. From 1988-1997, we prospectively collected data from 691 pregnanci es and 709 offspring of 488 women with Type I diabetes in a specific geogra phic area in Southern Finland, Glycated haemoglobin A(1c) at less than 14 w eeks of gestation was used as the indicator of glycaemic control. The malfo rmations were diagnosed either by ultrasonography in pregnancy or during th e neonatal period. We also studied 729 non-selected control pregnancies in women without diabetes. Results. The numbers of major fetal malformations were 30 (4.2%) in patient s with Type I diabetes and 10 (1.2%) in the control subjects (relative risk 3.1; 95% confidence interval: 1.6 to 6.2). Even women whose HbA(1c) was on ly slightly raised (5.6 to 6.8%, ie 2.0 to 5.9 standard deviation units) sh owed a relative risk of 3.0 (95% confidence interval: 1.2 to 7.5). Haemoglo bin A(1c) retained its statistically significant association with the occur rence of malformations after adjusting for White's class, age at onset of d iabetes, duration of diabetes, parity, smoking and participation in pre-pre gnancy counselling. Conclusions/interpretation. Even a slightly raised HbA(1c) during early pre gnancy in women with Type I diabetes carries an increased risk for fetal ma lformations. Therefore normoglycaemia should be strived for during early pr egnancy.