Prenatal weight gain patterns and spontaneous preterm birth among nonobese black and white women

To examine the relationship between prenatal weight gain and spontaneous preterm delivery, using the Institute of Medicine (IOM) guidelines.

Nonobese low-income black (677 subjects) and white (338) women were grouped by ethnicity and prepregnancy body mass index (BMI) as low (less than 19.8) or normal (19.8-26.0). The relationship of total gain (first trimester) and weekly rate of gain (second and third trimester) to spontaneous preterm delivery was determined while controlling for sociodemographic and reproductive variables as well as for time between last weight observation and delivery.

For all women combined, the mean (+/- standard deviation) weight gain during the first trimester was 2.48 +/- 3.36 kg, and the mean rate of gain during the second and third trimesters was 0.49 +/- 0.21 and 0.45 +/- 0.28 kg/week, respectively. Low first- or second-trimester weight gain was not associated with increased adjusted odds ratios (OR) for spontaneous preterm delivery. Third-trimester rates of gain below the lower limit of the IOM-recommended range (less than 0.38 kg/week with low BMI, less than 0.37 kg/week with normal BMI) were associated with increased preterm delivery among all women (OR 2.46, 95% confidence interval [CI] 1.53-3.92), all black women (OR 1.98, 95% CI 1.16-3.41), and all white women (OR 4.05, 95% CI 1.41-11.66).

These observations suggest that a low third-trimester rate of weight gain, defined using IOM guidelines, is associated with an increased risk of spontaneous preterm delivery among nonobese black and white women.