American Journal of Epidemiology Advance Access published online on May 1, 2008
American Journal of Epidemiology, doi:10.1093/aje/kwn092
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Original Contribution |
Obesity Subtypes and Risk of Spontaneous versus Medically Indicated Preterm Births in Singletons and Twins
1 Department of Epidemiology and Biostatistics, College of Public Health, University of South Florida, Tampa, FL
2 Department of Obstetrics and Gynecology, College of Medicine, University of South Florida, Tampa, FL
3 Department of Mathematics and Statistics, College of Arts and Sciences, University of South Florida, Tampa, FL
4 Department of Community and Family Health, College of Public Health, University of South Florida, Tampa, FL
5 Department of Epidemiology and Biostatistics, Arnold School of Public Health, University of South Carolina, Columbia, SC
Correspondence to Dr. Hamisu Salihu, Center for Research and Evaluation, Lawton and Rhea Chiles Center for Healthy Mothers and Babies, University of South Florida, 3111 East Fletcher Avenue, Tampa, FL 33613 (e-mail: hamisu.salihu{at}gmail.com).
Received for publication December 23, 2007. Accepted for publication March 18, 2008.
Using data from the Missouri maternally linked files (1989–1997), the authors examined the association among maternal obesity, obesity subtypes, and spontaneous and medically indicated preterm (<37 weeks) and very preterm (<33 weeks) births in singletons and twins. Adjusted odds ratios were obtained with correction for intracluster correlation. The prevalence of obesity increased by 77% over the study period (ptrend < 0.001). Obese mothers had a lower risk for spontaneous preterm birth, and this was more pronounced among twins (odds ratio = 0.68, 95% confidence interval: 0.62, 0.75) than singletons (odds ratio = 0.84, 95% confidence interval: 0.82, 0.87). However, this association was present only among obese women who gained less than 0.69 kg/week for singletons and between 0.23 and 0.69 kg/week for twins. By contrast, obese mothers with singleton gestation had about 50% greater odds of medically indicated preterm (odds ratio = 1.46, 95% confidence interval: 1.39, 1.54) and very preterm (odds ratio = 1.49, 95% confidence interval: 1.34, 1.65) births, and the risk increases with ascending severity of obesity (ptrend < 0.01). For extreme obesity, the risk of medically indicated preterm and very preterm births was almost double that for nonobese women. Similar findings were observed in twins. These data suggest that obesity increases the risk for medically indicated but not spontaneous preterm birth in both singletons and twins.
obesity; obstetric labor, premature; premature birth; twins
Abbreviations: BMI, body mass index; SD, standard deviation