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.