Associations of Maternal Diabetes and Body Mass Index With Offspring Birth Weight and Prematurity.

Importance: Maternal obesity, pregestational type 1 diabetes, and gestational diabetes have been reported to increase the risks for large birth weight and preterm birth in offspring. However, the associations for insulin-treated diabetes and non-insulin-treated type 2 diabetes, as well as the associations for joint diabetes disorders and maternal body mass index, with these outcomes are less well documented. Objective: To examine associations of maternal diabetes disorders, separately and together with maternal underweight or obesity, with the offspring being large for gestational age and/or preterm at birth. Design, Setting, and Participants: This population-based cohort study used nationwide registries to examine all live births (n = 649 043) between January 1, 2004, and December 31, 2014, in Finland. The study and data analysis were conducted from April 1, 2018, to October 10, 2018. Exposures: Maternal prepregnancy body mass index, pregestational diabetes with insulin treatment, pregestational type 2 diabetes without insulin treatment, and gestational diabetes. Main Outcomes and Measures: Offspring large for gestational age (LGA) at birth and preterm delivery. Logistic regression models were adjusted for offspring birth year; parity; and maternal age, country of birth, and smoking status. Results: Of the 649 043 births, 4000 (0.62%) were delivered by mothers who had insulin-treated diabetes, 3740 (0.57%) by mothers who had type 2 diabetes, and 98 568 (15.2%) by mothers who had gestational diabetes. The mean (SD) age of mothers was 30.15 (5.37) years, and 588 100 mothers (90.6%) were born in Finland. Statistically significant interactions existed between maternal body mass index and diabetes on offspring LGA and prematurity (insulin-treated diabetes: LGA F = 3489.0 and prematurity F = 1316.4 [P < .001]; type 2 diabetes: LGA F = 147.3 and prematurity F = 21.9 [P < .001]; gestational diabetes: LGA F = 1374.6 and prematurity F = 434.3 [P < .001]). Maternal moderate obesity, compared with normal-weight mothers with no diabetes, was associated with a mildly increased risk of having an offspring LGA (1069 [3.5%] vs 5151 [1.5%]; adjusted odds ratio [aOR], 2.45; 95% CI, 2.29-2.62), and mothers with insulin-treated diabetes had markedly elevated risks of having an offspring LGA (1585 [39.6%] vs 5151 [1.5%]; aOR, 43.80; 95% CI, 40.88-46.93) and a preterm birth (1483 [37.1%] vs 17 481 [5.0%]; aOR, 11.17; 95% CI, 10.46-11.93). Mothers who were moderately obese with type 2 diabetes were at increased risks of LGA (132 [16.4%] vs 5151 [1.5%]; aOR, 12.44; 95% CI, 10.29-15.03) and prematurity (83 [10.3%] vs 17 481 [5.0%]; aOR, 2.14; 95% CI, 1.70-2.69). Mothers who were moderately obese with gestational diabetes had a milder risk of LGA (1195 [6.7%] vs 5151 [1.5%]; aOR, 4.72; 95% CI, 4.42-5.04). Among spontaneous deliveries, the risks were strongest for moderately preterm births, but insulin-treated diabetes was associated with an increased risk also for very and extremely preterm births. Conclusions and Relevance: Maternal insulin-treated diabetes appeared to be associated with markedly increased risks for LGA and preterm births, whereas obesity in mothers with type 2 diabetes had mild to moderately increased risks; these findings may have implications for counseling and managing pregnancies.