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

https://doi.org/10.1016/j.ajog.2015.07.033Get rights and content

Objective

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.

Study Design

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.

Results

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).

Conclusion

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

Section snippets

Materials and Methods

The data analysis was approved by the University of California, San Francisco, Committee of Human Subjects Approval and the California State Committee of Human Subjects Protection. We built a cohort of women aged 12–44 years who received publicly funded contraceptive services in the 18 months after birth. 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.

Variables

This study explores whether contraceptive coverage and use within 18 months of the index birth were associated with decreased odds of a preterm birth. Contraceptive coverage estimates the amount of contraceptive supply that a woman received. The length of coverage is determined through applying an algorithm based on the specified method and the quantity dispensed (eg, the number of pill packs or condoms distributed) from pharmacy and on-site claims during the study period. For cases of method

Multivariable Model

We constructed a multivariate logistic model examining the relationship of contraceptive coverage with the outcome of preterm birth. Contraceptive coverage was defined as a continuous variable from 0–18 months. We controlled for demographic variables, including education level, race/ethnicity, nativity, age at index birth, and parity. We used software (SAS, version 9.2, PROC LOGISTIC; SAS Institute, Cary, NC) for all analyses.

Sample characteristics

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 (Table 1). Of these women, 9.8% had a preterm birth. Among women with a preterm birth, 86.9% were moderate to late preterm, 8.6% very preterm, and 4.5% extremely preterm births. In the study cohort, nearly 95% of the births were normal-weight infants.

Most of the women received user-dependent hormonal contraceptives as their most effective method (Table 2) (54,845;

Comment

Our findings demonstrate a small, but significant reduction in preterm births attributable to provision of postpartum contraception in a diverse cohort of Medicaid patients. We found that for every month of contraceptive coverage, odds of a preterm birth decrease by 1.1%. This finding compares favorably with estimates of preterm birth reduction due to other interventions.11 For example, broadly implementing smoking cessation and progesterone supplementation interventions would have an estimated

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    Supported by the Office of Family Planning, Department of Health Care Services, State of California, contract number 12-89338 A2.

    The authors report no conflict of interest.

    All analyses, interpretations, and conclusions reached are those of the University of California, San Francisco, and not necessarily of the State of California.

    Cite this article as: Rodriguez MI, Chang R, Thiel de Bocanegra H. The impact of postpartum contraception on reducing preterm birth: findings from California. Am J Obstet Gynecol 2015;213:703.e1-6.

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