Preterm birth is a leading cause of infant mortality, morbidity, and long-term disability, and these risks increase with decreasing gestational age.
Obesity increases the risk of preterm delivery, but the associations between overweight and obesity and subtypes of preterm delivery are not clear.
Dr Sven Cnattingius and colleagues studied the associations between early pregnancy body mass index (BMI) and risk of preterm delivery by gestational age and by precursors of preterm delivery.
The team performed a population-based cohort study of women with live singleton births in Sweden from 1992 through 2010.
Maternal and pregnancy characteristics were obtained from the nationwide Swedish Medical Birth Register.
|Risk of extremely preterm delivery increased with BMI among obese women|
|Journal of the American Medical Association|
The team's main outcomes included risks of preterm deliveries.
These outcomes were further characterized as spontaneous, and medically indicated preterm delivery.
Risk estimates were adjusted for maternal age, parity, smoking, education, height, mother's country of birth, and year of delivery.
Among 1,599,551 deliveries with information on early pregnancy BMI, 3082 were extremely preterm, 6893 were very preterm, and 67,059 were moderately preterm.
The team noted that risks of extremely, very, and moderately preterm deliveries increased with BMI, and the overweight and obesity-related risks were highest for extremely preterm delivery.
The research team found that among normal-weight women, the rate of extremely preterm delivery was 0.17%.
As compared with normal-weight women, rates and adjusted odds ratios of extremely preterm delivery were BMI 25 to less than 30, BMI 30 to less than 35, BMI 35 to less than 40, and BMI of 40 or greater.
Risk of spontaneous extremely preterm delivery increased with BMI among obese women.
The team found that risks of medically indicated preterm deliveries increased with BMI among overweight and obese women.
Dr Cnattingius' team concludes, "In Sweden, maternal overweight and obesity during pregnancy were associated with increased risks of preterm delivery, especially extremely preterm delivery."
"These associations should be assessed in other populations."