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196: The effect of maternal weight on postterm delivery

      Objective

      To assess the effect of prepregnancy BMI and weight gain on postterm delivery.

      Study Design

      This is a retrospective cohort study utilizing birth records linked to hospital discharge data for all term, singleton infants > 37 weeks gestation born to Missouri residents (1993-1999), excluding infants born to mothers with diabetes or chronic hypertension or a history of previous cesarean section. The primary outcome was delivery at 42 weeks gestation. Pre-pregnancy BMI was categorized as follows: normal (referent), overweight, and obese. Maternal weight gain based on Institute of Medicine (IOM) guidelines adjusted for pre-pregnancy weight.

      Results

      There were 416,358 births meeting study criteria. 8542 infants (2%) were born at 42 weeks gestation. Multivariable analysis was performed that controlled for maternal ethnicity, age, education, parity, tobacco history, Medicaid status, and infant sex. Being underweight and gaining less than the weight recommended by the IOM decreased the risk of postterm delivery. Being overweight and gaining more than the recommended weight increased the risk of postterm delivery.
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      Conclusion

      Elevated weight gain and pre-pregnancy weight increase the risk of a postterm delivery while low weight gain and pre-pregnancy weight decrease the risk of a postterm delivery. While most women do not get preconceptional care, our findings suggest that restricting weight gain to the normal range can reduce the risk of postterm pregnancy.