Infant mortality rates increased from 2.4/1000 among normal
weight women (BMI 18.5–24.9) to 5.8/1000 among women with obesity
grade 3 (BMI ≥40.0). Compared with normal weight, overweight (BMI
25.0–29.9) and obesity grade 1 (BMI 30.0–34.9) were associated with
modestly increased risks of infant mortality (adjusted odds ratios 1.25
(95% confidence interval 1.16 to 1.35) and 1.37 (1.22 to 1.53),
respectively), and obesity grade 2 (BMI 35.0–39.9) and grade 3 were
associated with more than doubled risks (adjusted odds ratios 2.11 (1.79
to 2.49) and 2.44 (1.88 to 3.17)). In analyses stratified by preterm and
term births, maternal BMI was related to risks of infant mortality primarily
in term births (≥37 weeks), where risks of deaths due to birth asphyxia
and other neonatal morbidities increased with maternal overweight and
obesity. Obesity grade 2–3 was also associated with increased infant
mortality due to congenital anomalies and sudden infant death syndrome.