WEDNESDAY, July 21 (HealthDay News) -- Overweight and obese women appear to be at greater risk of delivering preterm babies, and, after publication bias is taken into account, maternal overweight and obesity do not have beneficial effects on low infant birth weight, according to research published July 20 in BMJ.

Sarah D. McDonald, M.D., of McMaster University in Hamilton, Canada, and colleagues studied data on 1,095,834 women from 84 published studies to determine the effect of maternal overweight and obesity on preterm birth (before 37 weeks' gestation) and low birth weight (less than 2,500 g) in singleton pregnancies in both developed and developing countries.

The researchers found the risk of preterm birth to be similar between overweight/obese mothers and those of normal weight, but the risk of induced preterm birth was higher in overweight/obese women (relative risk [RR], 1.30). The risk of delivering a low birth weight baby was less for overweight/obese women (RR, 0.84), more so in developing countries than in developed nations (RR, 0.58 versus 0.90). This apparent protective element, however, disappeared after accounting for publication bias and with the addition of imputed "missing" studies (RR, 0.95), while the risk of preterm birth appeared to be significantly higher in overweight/obese women after accounting for publication bias (RR, 1.24).

"Clinicians need to be aware that overweight or obesity in women is not protective against having infants of low birth weight and should consider surveillance when indicated. Ideally, overweight or obese women should have pre-pregnancy counseling so that they are informed of their perinatal risks and can try to optimize their weight before pregnancy," the authors write.

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