Effect of maternal weight on postterm delivery.

Objective—Examine the effect of prepregnancy weight and maternal gestational weight gain on postterm delivery rates. Methods—This was a retrospective cohort study of term, singleton births (N=375,003). We performed multivariable analyses of the association between postterm pregnancy and both prepregnancy body mass index (BMI) and maternal weight gain. Results—Prolonged or postterm delivery (41 or 42 weeks) was increasingly common with increasing prepregnancy weight (p<0.001) and increasing maternal weight gain (p<0.001). Underweight women were 10% less likely to deliver postterm than normal weight women who gain within the recommendations (aOR 0.90 (95% CI 0.83, 0.97)). Overweight women who gain within or above recommendations were also at increased risk of a 41 week delivery. Finally, obese women were at increased risk of a 41 week delivery with increasing risk with increasing weight (below, within, and above recommendations aOR 1.19, 1.21, and 1.27, respectively). Conclusion—Elevated prepregnancy weight and weight gain both increase the risk of a postterm delivery. While most women do not receive preconceptional care, restricting weight gain to the within the recommended range can reduce the risk of postterm pregnancy in normal, overweight, and obese women.