Spontaneous and indicated preterm delivery in pregestational diabetes mellitus: Etiology and risk factors

Objective: To characterize the indications for preterm delivery and identify risk factors predicting preterm delivery in pregnancies complicated by pregestational diabetes (PGDM). Study design: A retrospective cohort study of all women with type 1 or type 2 diabetes mellitus followed from preconception to delivery at our institute from 1996 to 2004 (study group). Rates of spontaneous and indicated preterm delivery were compared with a control group of nondiabetic women. Results: Rates of preterm delivery were 26.6% (119/448) and 6.0% (1,038/17,370) in the study and control groups, respectively (P < 0.001). The PGDM group had higher rates of both spontaneous (6.9% vs. 4.8%, P < 0.001) and indicated (19.6% vs. 1.2%, P < 0.001) preterm deliveries. Most of the preterm deliveries in the PGDM group were indicated (73.9%) compared with 20.1% in the control group (P < 0.001). Preeclampsia was the most significant factor associated with indicated preterm delivery in the PGDM group (OR = 11.7, 95% CI = 3.3-41.7), followed by nephropathy, nulliparity, HbA1c levels prior to conception and prior to delivery, duration of diabetes, prepregnancy body mass index and weight gain during pregnancy. Spontaneous preterm delivery was related to duration of diabetes, presence of nephropathy, and previous preterm delivery. Conclusion: The risk of both spontaneous and indicated preterm delivery is increased in pregnancies complicated by PGDM. Except for glycemic control, none of the risk factors identified is modifiable by preconception or antenatal care.