Repeat pregnancies after a short interpregnancy interval are common and are associated with negative maternal and infant health outcomes. Few studies have examined the relative effectiveness of postpartum contraceptive choices.

We aimed to determine the initiation trends and relative effectiveness of postpartum contraceptive methods, with typical use, on prevention of short delivery intervals (≤27 months) among women with access to universal healthcare, including coverage that entails no co-payments and allows unlimited contraceptive method switching.

This retrospective cohort study included women who were enrolled in the United States military healthcare system who were admitted for childbirth between October 2010 and March 2015, with ≥6 months postpartum enrollment. With the use of insurance records, we determined the most effective contraceptive method initiated during the first 6 months after delivery, even if subsequently discontinued. Rates of interdelivery intervals of ≤27 months, as proxies for interpregnancy intervals ≤18 months, were determined with the use of the Kaplan-Meier estimator. Women who were disenrolled, who reached 27 months after delivery without another delivery, or who reached the end of the study period were censored. The influence of sociodemographic variables and contraceptive choices on time to subsequent delivery was evaluated by Cox regression analysis, which accounted for a possible correlation among multiple deliveries by an individual woman.

During the study timeframe, 373,840 women experienced a total of 450,875 postpartum intervals. Women averaged 27 (standard deviation, 5.3) years of age at the time of delivery; 33.9% of them were <25 years old; 15.5% of them were active duty service members, and 31.6% of them had insurance sponsors of junior enlisted rank (which suggests lower income). Postpartum contraceptive methods that were initiated included self or partner sterilization (7%), intrauterine device (13.5%), etonogestrel implant (3.4%), depot medroxyprogesterone acetate (2.5%), and pill, patch, or ring (36.8%). Furthermore, 36.7% of them did not initiate a prescription method. Etonogestrel implant initiation increased from 1.7% of postpartum women in the first year of our study to 5.3% in the final year. The estimated short interdelivery interval rate was 17.4%, but rates varied with contraceptive method: 1% with sterilization, 6% with long-acting reversible contraception, 12% with depot medroxyprogesterone, 21% with pill, patch, or ring, and 23% with no prescription method. In a multivariable analysis, the adjusted hazard of a short interdelivery interval was highest among women who were younger, on active duty, or with officer insurance sponsors. Compared with nonuse of any prescription contraceptive, the use of an intrauterine device reduced the hazard of a subsequent delivery (adjusted hazard ratio, 0.19; 95% confidence interval, 0.18–0.20), as did etonogestrel implant (adjusted hazard ratio, 0.21; 95% confidence interval, 0.19–0.23); the pill, patch, or ring had less effect (adjusted hazard ratio, 0.80; 95% confidence interval, 0.78–0.81).

Postpartum initiation of long-acting reversible contraception is highly effective at the prevention of short interdelivery intervals, whereas pill, patch, or ring methods are associated with rates of short interdelivery intervals similar to users of no prescription contraception. This study supports long-acting reversible contraception as first-line recommendations for postpartum women who wish to retain fertility but avoid early repeat pregnancy.