Impact of weight loss between pregnancies on recurrent preterm birth

Low maternal pre-pregnancy body-mass index (BMI) has been associated with preterm birth (PTB). Women delivering preterm are at increased for recurrent PTB. Our goal was to determine whether change in BMI between pregnancies alters the risk of PTB.

From our electronic perinatal database, we identified women who delivered consecutive pregnancies at our institution. Women were grouped by prepregnancy BMI category (underweight: <18.5, normal: 18.5-24.9, overweight: 25-29.9, obese: >30 kg/m2). They were then grouped based on change in actual BMI ("increase": >5 kg/m2, "stable": within 5 kg/m2, "decrease": >5 kg/m2) and change in BMI category between pregnancies. The risk of PTB was correlated to change in BMI. P < .05 was considered significant.

One thousand two hundred forty-one women met inclusion criteria. Women with a PTB in their first pregnancy had more PTB in their second than those with a term birth in their first pregnancy (33.6% vs 8.0%, P < .001). Women whose BMI decreased more than 5 kg/m2 had more frequent PTB in the second pregnancy than those who did not (21.1% vs 9.3%, P = .01). For those with a term birth in the first pregnancy, PTB in the second did not increase with declining BMI. However, for women with a PTB in the first pregnancy, PTB was more frequent in the second if their BMI decreased a BMI category (53.8% vs 27.6%, P = .05) or if BMI decreased more than 5 kg/m2 (80.0% vs 28.2%, P = .01).

Women whose BMI declines between pregnancies are at increased risk for PTB, particularly if they delivered a prior preterm gestation.