The epidemiology of threatened preterm labor: A prospective cohort study

Objective: The purpose of this study was to describe the occurrence, timing, and outcomes of hospital-based diagnoses of preterm labor. Study design: Administrative records identified hospital admissions for preterm labor among 2534 women in an ongoing cohort study. Factors that were considered risks for prematurity were examined by logistic regression for an association with any preterm labor diagnosis, a preterm labor diagnosis <33 weeks of gestation, or ≥33 weeks of gestation. Results: Of 234 women (9%) who experienced hospitalization for preterm labor, 90 women (38%) were delivered in the first episode. Previous preterm birth consistently was associated with a diagnosis of preterm labor. Reporting a sexually transmitted infection (odds ratio, 1.8; 95% CI, 1.1-3.0) or bacterial vaginosis (odds ratio, 2.6; 95% CI, 1.7-4.1) early in pregnancy was associated with hospitalization for preterm labor between 24 and 32 weeks of gestation. Conclusion: The incidence of first-time hospitalization for preterm labor was 9%, with most episodes not resulting in preterm birth. Previous preterm birth was associated therefore with a preterm labor diagnosis.