Maternal Prepregnancy Body Mass Index and Delivery of a Preterm Infant in Missouri 1998–2000


Teresa S. Johnson, College of Nursing, University of Wisconsin-Milwaukee, P. O. Box 413, Milwaukee, WI 53201. E-mail:


ABSTRACT Objective: To determine risk of delivering a preterm infant (<37 weeks) in overweight/obese women.

Design: Descriptive.

Sample: Population-based sample of 169,881 singleton Missouri birth certificate records for 1998–2000.

Measures: Prepregnancy body mass index (BMI): underweight BMI<19.8; normal BMI=19.8–24.9; overweight BMI=25–29.9; and obese BMI≥30; and preterm birth (<37 completed weeks' gestation).

Results: In each BMI category, the percent of women who delivered a preterm infant is: underweight 11.5%, normal 8.3%, overweight 8.2%, and obese 8.5%. For women with a BMI of overweight (odds ratio [OR] 0.9, 95% confidence interval [CI]=0.8–0.9) and obese (OR 0.8, 95% CI=0.8–0.9), the risk of delivering a preterm infant decreased when compared with women with a BMI<19.8. Black (OR=2.5, 95% CI 2.4–2.6) and Hispanic (OR=1.4, 95% CI 1.2–1.5) women had a higher risk of preterm birth than White women when obesity, diabetes, hypertension, and prenatal care were controlled. Women with diabetes (OR=1.4, 95% CI=1.2–1.5), hypertension (OR=3.2, 95% CI=3.1–3.4), and those who smoked (OR=1.6, 95% CI=1.6–1.7) were at increased risk for a preterm birth.

Conclusions: Findings suggest that preconception and prenatal care focus on identification and management of risks associated with premature births and maternal risk factors such as diabetes, hypertension, and smoking.