The impact of postpartum contraception on reducing preterm birth: findings from California

Family planning is recommended as a strategy to prevent adverse birth outcomes. The potential contribution of postpartum contraceptive coverage to reducing rates of preterm birth is unknown. In this study, we examine the impact of contraceptive coverage and use within 18 months of a birth on preventing preterm birth in a Californian cohort.

We identified records for second or higher-order births among women from California's 2011 Birth Statistical Master File and their prior births from earlier Birth Statistical Master Files. To identify women who received contraceptive services from publicly funded programs, we applied a probabilistic linking methodology to match birth files with enrollment records for women with Medi-Cal or Family Planning, Access, Care, and Treatment Program (PACT) claims. The length of contraceptive coverage was determined through applying an algorithm based on the specified method and the quantity dispensed. Preterm birth was defined as a birth occurring <37 weeks' gestation, and calculated from the medical record. We further examined differences in preterm birth using subcategories defined by the World Health Organization: extremely preterm (<28 weeks); very preterm (28 to <32 weeks); and moderate to late preterm (32 to <37 weeks). We built a multivariable regression model to examine the effect of contraceptive coverage on the odds of a preterm birth and control for key covariates.

The cohort consisted of 111,948 women who were seen at least once by a Medi-Cal or Family PACT provider within 18 months of delivery. Of the cohort, 9.75% had a preterm birth. Contraceptive coverage was found to be protective against preterm birth. For every month of contraceptive coverage, odds of a preterm birth <37 weeks decrease by 1.1% (odds ratio, 0.989; 95% confidence interval, 0.986-0.993).

Improving postpartum contraceptive use has the potential to reduce preterm births.