Factors affecting fetal weight distribution in women with type I diabetes

Objective To identify factors independently affecting fetal weight in women with type I diabetes. Simpson Memorial Maternity Hospital, Edinburgh. Design Prospectively recorded data in consecutive women with type I diabete s, between 1975-1992. Setting Simpson Memorial Maternity Hospital, Edinburgh. Population Three hundred and two pregnancies with type I diabetes identifie d before pregnancy, with antenatal care and delivery in the Simpson Memoria l Maternity Hospital, a singleton pregnancy, and the same diabetic physicia n. Methods Normal ranges for birthweight were established for the total hospit al population. All cases and the total population had pregnancy dating by u ltrasound. The relation between standardised birthweight and explanatory va riables was investigated using correlation analysis, t tests and chi(2) tes ts as appropriate, and subsequently using multiple linear regression. Resul ts Standardised birthweight in cases, compared with the reference populatio n,showed a unimodal, approximately normal distribution, markedly shifted to the right (mean + 1.26 SD). The most predictive variable was glycated haem oglobin concentration at 27-33 weeks, which explained 6.3% of the birthweig ht variance, while smoking explained 2.7% and maternal weight 2.0%. There w as a trend towards a negative relationship with glycated haemoglobin concen tration at 6-12 weeks. Smoking and glycated haemoglobin concentration were strongly intercorrelated. Conclusions Most of the variance in standardised birthweight remains unexpl ained, but glycated haemoglobin concentration at 27-33 weeks is the most po werful explanatory variable. Possible reasons why there is not a stronger r elationship between markers of maternal glycaemia and birthweight are discu ssed.