Researchers from McMaster University in Hamilton pooled data from 84 studies involving more than 1 million women and found that the heavier the mother's weight, the greater the risk of preterm birth.
The analysis initially showed no difference in the overall risk of early delivery (before 37 weeks) associated with body weight. But after adjusting for bias, researchers found that being overweight or obese was associated with a 30% increased risk for early delivery.
Researchers found that the risk for very early delivery (before 32 weeks) and induced early delivery before 37 weeks increased with maternal weight. Compared to normal-weight women, the risk for both outcomes was about 15%, 50% and 80% higher, respectively, among overweight, obese, and very obese women.
Early deliveries are more common among overweight and obese women, since their risk for pregnancy-related complications is so much greater.
Thus far studies examining the impact of maternal body weight on early birth and low birth weight have been mixed, with some finding an increased risk for the complications and others finding no such risk. In a few studies, maternal obesity seemed to be protective against delivering a low-birth-weight baby.
The study was published in the British Medical Journal.
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