OBJECTIVE -Women with type 2 and type 1 diabetes have differing risk factors for pregnancy loss. We compared the rates and causes of pregnancy loss in women with type 1 and type 2 diabetes.RESEARCH DESIGN AND METHODS -We utilized prospectively collected data on all pregnancies in a 20-year period (1986 -2005) from a single center with a high prevalence of type 2 diabetes. Pregnancy losses included terminations for medical reasons and deaths up to 1 month postpartum but not spontaneous pregnancy losses Ͻ20 weeks' gestation.RESULTS -There were 870 pregnancies in women with known diabetes (330 with type 1 and 540 with type 2 diabetes) and 325 in women with diabetes diagnosed in pregnancy but persisting postpartum (97% type 2 diabetes). The rate of pregnancy loss was similar in type 1 and type 2 diabetes (2.6 vs. 3.7%, P ϭ 0.39), but the causes of pregnancy loss differed. In type 1 diabetes Ͼ75% were attributable to major congenital anomalies or prematurity; in type 2 diabetes Ͼ75% were attributable to stillbirth or chorioamnionitis (P ϭ 0.017). Women with type 2 and type 1 diabetes had similar A1C at presentation and near term, but the former were older (P Ͻ 0.001) and more obese (P Ͻ 0.0001).CONCLUSIONS -There are significant differences in the main causes of pregnancy loss in women with type 1 and type 2 diabetes. The higher rates of stillbirth in women with type 2 diabetes, suggest that other features, such as obesity, contribute significantly to pregnancy losses. Diabetes Care 30:2603-2607, 2007B efore the discovery of insulin, a woman with type 1 diabetes had almost no chance of successful delivery of a healthy baby. With the advent of insulin treatment, pregnancy losses continued to be high, predominantly through stillbirth, but neonatal deaths due to congenital malformation, birth trauma, hypoglycemia, and respiratory distress syndrome all took their toll (1). Substantial improvement in the rates of perinatal mortality followed the development of centralized care and regimens focused on achieving strict glycemic control and ensuring early delivery (2,3). Several centers have reported stillbirth rates in women with type 1 diabetes that are comparable to those in nondiabetic women (4 -7). Pregnancy losses due to congenital anomalies (resulting from poor glycemic control in early pregnancy) have proven harder to reduce, so terminations of pregnancy or neonatal death resulting from severe congenital anomalies now account for a large proportion of pregnancy losses in women with type 1 diabetes (6,8,9).The developing epidemic of obesity over the last two decades has seen a substantial reduction in the age of onset of type 2 diabetes and its emergence in women of childbearing age. In many areas of the world, the number of pregnancies in women with type 2 diabetes now exceeds that of women with type 1 diabetes (6,10 -13). A number of centers have reported higher rates of stillbirth or congenital anomalies in type 2 diabetic pregnancy, suggesting that the outcomes of pregnancy in type 2 diabetes can be worse than tha...