Perinatal and Infant Mortality in Term and Preterm Births Among Women With Type 1 Diabetes

Most previous studies have shown that women with pregestational type 1 diabetes are at considerably higher risk of pregnancy complications and adverse pregnancy outcomes compared with women without diabetes. Few population-based studies have investigated the risk of perinatal death among women with type 1 diabetes separately in term and preterm births. The primary aim of this population-based study was to compare the risk of stillbirth, infant death, preterm delivery, and preeclampsia between women with pregestational type 1 diabetes and a background population of women without diabetes. A secondary aim was to examine the risks of adverse birth outcomes in preterm and term deliveries separately. Data were obtained by linking the Medical Birth Registry of Norway and the Norwegian Childhood Diabetes Registry for all births occurring after 22 weeks of gestation between 1985 and 2004. The study cohort included 1307 babies born to mothers with type 1 diabetes in the Diabetes Registry during the study period; the background comparison group included 1,161,092 babies born during the same period to mothers without type 1 diabetes. Logistic regression was used to estimate risks of adverse birth outcomes in the 2 groups, adjusting for potential confounding variables. Stillbirth and perinatal death occurred about 3 times more often among the pregnancies in women with type 1 diabetes than those in the background population; the odds ratio (OR) for stillbirth (≥22 weeks of gestation) was 3.6 (95% confidence interval [CI], 2.5–5.3) and for perinatal death (stillbirth or death in the first week of life) was 2.9 (95% CI, 2.0–4.1). The risk of infant death in the first year of life in the diabetes group was twice that of the background population (OR, 1.9; 95% CI, 1.1–3.2). With respect to preterm birth (<37 weeks of gestation) and preeclampsia, the risks were approximately 5 to 6 times higher; the ORs were 4.9 (95% CI, 4.3–5.5) and 6.3 (95% CI, 5.5–7.2), respectively. Adjustment for potential confounding variables had little effect on the data. Stratified analyses of the risk of mortality and other adverse birth outcomes separately for preterm and term births showed that the excess mortality risk was confined to term births with approximately a 5-fold increased risk of stillbirth and infant mortality. These findings show a substantially higher risk of adverse pregnancy outcomes, including infant death, among women with pregestational type 1 diabetes compared with the background population. The increased risk of adverse outcomes appears limited to term births.