Obesity, assisted reproductive technology, and early preterm birth--Florida, 2004-2006.

Florida resident birth certificates for 2004-2006 were linked to the Centers for Disease Control and Prevention's National ART Surveillance System and were used to investigate 1) whether the association of assisted reproductive technology (ART) with preterm birth varies by prepregnancy body mass index and 2) whether the association varies by plurality. Preterm birth was defined as early preterm birth (gestation <34 weeks) and late preterm birth (gestation 34-36 weeks). Descriptive statistics and multinomial logistic regression were used to explore maternal and infant differences by ART status and plurality. Of 581,403 women included in the study, 24.0% were overweight, 18.6% were obese, 7.3% had late preterm birth, 2.6% had early preterm birth, and 0.67% conceived through ART. Among singleton births, ART was associated with increased early preterm birth risk among underweight (odds ratio (OR) = 2.94, 95% confidence interval (CI): 1.27, 6.81), overweight (OR = 1.75, 95% CI: 1.12, 2.72), and obese (OR = 2.37, 95% CI: 1.51, 3.71) women. Among twins, ART was significantly associated with increased risk among overweight (OR = 1.61, 95% CI: 1.12, 2.32) and obese (OR = 1.85, 95% CI: 1.18, 2.90) women. Differences in the associations between ART and early preterm birth by body mass index and plurality warrant further investigation.