Maternal prepregnancy body mass index and risk of spontaneous preterm birth

Paediatr Perinat Epidemiol. 2014 Jul;28(4):302-11. doi: 10.1111/ppe.12125. Epub 2014 May 9.

Abstract

Background: Findings from studies examining risk of preterm birth associated with elevated prepregnancy body mass index (BMI) have been inconsistent.

Methods: Within a large population-based cohort, we explored associations between prepregnancy BMI and spontaneous preterm birth across a spectrum of BMI, gestational age, and racial/ethnic categories. We analysed data for 989,687 singleton births in California, 2007-09. Preterm birth was grouped as 20-23, 24-27, 28-31, or 32-36 weeks gestation (compared with 37-41 weeks). BMI was categorised as <18.5 (underweight); 18.5-24.9 (normal); 25.0-29.9 (overweight); 30.0-34.9 (obese I); 35.0-39.9 (obese II); and ≥ 40.0 (obese III). We assessed associations between BMI and spontaneous preterm birth of varying severity among non-Hispanic White, Hispanic, and non-Hispanic Black women.

Results: Analyses of mothers without hypertension and diabetes, adjusted for age, education, height, and prenatal care initiation, showed obesity categories I-III to be associated with increased risk of spontaneous preterm birth at 20-23 and 24-27 weeks among those of parity 1 in each race/ethnic group. Relative risks for obese III and preterm birth at 20-23 weeks were 6.29 [95% confidence interval (CI) 3.06, 12.9], 4.34 [95% CI 2.30, 8.16], and 4.45 [95% CI 2.53, 7.82] for non-Hispanic Whites, non-Hispanic Blacks, and Hispanics, respectively. A similar, but lower risk, pattern was observed for women of parity ≥ 2 and preterm birth at 20-23 weeks. Underweight was associated with modest risks for preterm birth at ≥ 24 weeks among women in each racial/ethnic group regardless of parity.

Conclusions: The association between women's prepregnancy BMI and risk of spontaneous preterm birth is complex and is influenced by race/ethnicity, gestational age, and parity.

Keywords: low weight; obesity; pregnancy; race disparity.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • African Americans / statistics & numerical data
  • Body Mass Index*
  • California
  • Cohort Studies
  • European Continental Ancestry Group / statistics & numerical data
  • Female
  • Gestational Age
  • Hispanic Americans / statistics & numerical data
  • Humans
  • Obesity / complications*
  • Obstetric Labor, Premature / epidemiology*
  • Obstetric Labor, Premature / etiology
  • Parity
  • Pregnancy
  • Pregnancy Complications / epidemiology
  • Pregnancy Complications / etiology
  • Premature Birth / epidemiology*
  • Premature Birth / ethnology
  • Premature Birth / etiology