Short Interpregnancy Intervals: Results from the First Baby Study.

BACKGROUND: Short interpregnancy interval (SIPI), defined as 18 months or fewer between delivery and subsequent conception, has become an independent marker of maternal and child health.

METHODS: We performed a secondary analysis of 18 months of data from The First Baby Study, a prospective cohort of women followed from pregnancy through 3 years after their first birth. Women with SIPIs by 6, 6 to 12, and 12 to 18 months were compared with those without conceptions at those times. We then analyzed pregnancy intention of the subpopulation of women with a SIPI of 18 months or fewer. Logistic regression analyses determined associations between maternal characteristics, including sociodemographic and reproductive indicators, and SIPI incidence and intention.

FINDINGS: Of 3,006 participants, 795 (26.5%) had a repeat pregnancy within 18 months: 58 (1.9%) occurred within 6 months, 242 (8.1%) between 6 and 12 months, and 495 (16.5%) between 12 and 18 months. Incidence of SIPI at each interval differed by maternal characteristics, including income, marital status, and intention. Most women (84%) with a SIPI of 6 months or less classified them as unintended. Less than 2% of women with SIPIs of 18 months or fewer reported any contraceptive use in the postpartum period and no pregnancies occurred with the use of very effective methods, including long-acting reversible contraception.

CONCLUSIONS: The population of women at risk for SIPI is not homogenous. Among those with SIPIs, there is a stark contrast in intention between those who conceive early (≤6 months) versus later (≥12 months). Given that almost no pregnancies occurred when women used postpartum contraception, contraceptive counseling and unfettered access should be available for those at greatest risk for an early, repeat, unintended pregnancy.