Rates of recurrent preterm birth by maternal body habitus in women receiving 17α-hydroxyprogesterone caproate

Objective: To examine the influence of maternal pre-pregnancy body mass index (BMI) on the rates of recurrent spontaneous preterm birth (SPTB) in women receiving 17α-hydroxyprogesterone caproate (17P). Methods: Retrospective analysis of a cohort of 6253 women with a singleton gestation and prior SPTB enrolled in 17P home administration program between 16.0 and 26.9 weeks. Data were grouped by pre-pregnancy BMI (lean <18.5kg/m², normal 18.5-24.9kg/m², overweight 25-29.9kg/m² and obese 30.0kg/m²). Delivery outcomes were compared using χ² and Kruskal-Wallis tests with statistical significance set at p<0.05. Results: SPTB<28 weeks was significantly lower in normal weight women. Rates of recurrent SPTB<37 weeks were highest in the group with BMI<18.5kg/m². Lean gravidas were younger, more likely to smoke, and less likely to be African-American than those with normal or increased BMI. In logistic regression, after controlling for race and prior preterm birth <28 weeks, the risk of SPTB<37 weeks decreased 2% for every additional 1kg/m² increase in BMI. Conclusions: Recurrent spontaneous preterm delivery<37 weeks in patients on 17P is more common in lean women (BMI<18.5kg/m²), and less common in obese women (BMI 30kg/m ²) suggesting that the current recommended dosing of 17P is adequate for women with higher BMI.