Aims: To assess pregnancy outcomes, in particular birthweight, in a large population-based cohort of women in Scotland with pre-gestational insulin-treated diabetes mellitus.
Methods: Data about diabetes from the Diabetes UK cohort were linked to data on births from the Scottish Hospital In-Patient Record System. This identified 1112 eligible singleton deliveries during 1979-95 to 706 insulin-treated women.
Results: One thousand and eighty-four (97.5%) deliveries resulted in a live-born infant and 28 (2.5%) in a stillbirth. There were 13 (1.2%) neonatal deaths. The mean birthweight of the live-born infants was 3421 g, 1.06 standard deviations greater than that of infants in the Scottish general population after correcting for sex and gestational age. Forty-three per cent of live-born babies in the study were large (> Scottish 90th percentile) and 4% small (< 10th percentile) for their sex and gestational age. Macrosomia, defined as birthweight > or = 4000 g, occurred in 23% live-born babies and its prevalence was significantly inversely related to duration of maternal diabetes. However, the mean birthweight of infants born to mothers with diabetes for 20 or more years was still 0.90 standard deviations greater than in the general population. Prevalence of macrosomia increased with increasing number of previous pregnancies, but was not associated with maternal height or smoking habits. Stillbirth and neonatal death rates were, respectively, 4.7 (95% confidence interval = 3.3, 6.8) and 2.4 (1.4, 4.1), times higher than those in the general population.
Conclusions: The frequency of adverse pregnancy outcomes in women with pre-existing insulin-treated diabetes was much higher than in the Scottish general population, and changed little during the study period. A detailed quantification of the independent effect of duration of mother's diabetes on birthweight revealed a continuous inverse correlation between these two variables.