714: Association between BMI < 20 and preterm birth

Abstract

Low maternal body mass index (BMI) has been associated with preterm birth (PTB) in previous unadjusted analyses. The mechanism behind this association is poorly understood. Our aim is to investigate the association between BMI < 20 and preterm birth. Our secondary aim is to examine the association between low BMI and serum inflammatory cytokines, cervical length, and birth weight. This is a secondary analysis of a multicenter, prospective cohort study designed to evaluate risk factors for preterm birth. Pre-pregnancy maternal BMI was the dependent variable, categorized as BMI < 20, 20-24.9, 25-29.9, >30. Primary outcome was preterm birth < 37 weeks of gestation. Secondary outcomes were preterm birth < 34 weeks of gestation; inflammatory cytokine levels; cervical length at 24 weeks of gestation; birth weight; diagnosis of small-for-gestational-age; validated maternal stress, anxiety, and depression scores. Descriptive statistics were generated. Multivariable logistic regression was used to analyze the data for the primary outcome, with results reported as adjusted odds ratios (aOR) and 95% confidence intervals (CI) and with BMI 20-24.9 as the reference group. Multivariable linear regression was used to analyze continuous secondary outcomes, and multivariable logistic regression was used to analyze categorical secondary outcomes. There were 2,980 women included in the analysis. 452 women had a BMI < 20. Groups differed significantly in age, percent nulliparous, and weight gain over pregnancy. Women with BMI < 20 were statistically more likely than women with a BMI of 20-24.9 to deliver < 37 weeks of gestation (aOR 1.97, CI 1.15, 3.38). They were also statistically more likely to have neonates with a lower birth weight (adjusted difference 159g, p<.001). C-reactive protein at 24 weeks of gestation was statistically different among women with BMI < 20. No other secondary outcomes were statistically significant. This study showed women with BMI < 20 have an increased risk for preterm birth < 37 weeks of gestation.