Objective Obesity and cervical insufficiency are leading causes of morbidity in pregnancy. We assess the relationship between maternal body mass index (BMI) and second-trimester cervical length. Methods A secondary analysis of a nested case-control study of women with singleton gestations enrolled from 2006 to 2008. The primary exposure was first-trimester BMI, categorized per World Health Organization criteria: normal (18.5 to ≤ 25 kg/m2), overweight (25 to ≤ 30 kg/m2), and obese (> 30 kg/m2). The primary outcome was cervical length > 75th percentile. Results Among 391 pregnant women observed, the median cervical length was 3.6 cm, and the median BMI was 24.8 kg/m2. In multivariable analyses, after adjusting for BMI, age, race, parity, smoking, and gestational age at delivery, women who were overweight (adjusted odds ratio [AOR]: 2.18; 95% CI: 1.20-3.96) and obese (AOR: 2.83; 95% CI: 1.47-5.43) were more than two times more likely to have a cervical length > 75th percentile. When cervical length and BMI were assessed linearly, for each 1.0 kg/m2 increase in BMI, cervical length increased by 0.25 mm. These results were robust to utilizing different cutoffs of cervical length and pre-pregnancy BMI. Conclusion This study demonstrates a relationship between BMI and cervical length suggesting that obesity may be associated with longer cervical length. These results will need to be replicated in larger cohorts undergoing universal cervical length assessment.
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