Interpregnancy interval after live birth or pregnancy termination and estimated risk of preterm birth: a retrospective cohort study

Abstract

Objectives: We assessed whether interpregnancy interval (IPI) length after live birth and after pregnancy termination was associated with preterm birth (PTB).

Design: Multiyear birth cohort.

Settings: Fetal death, birth and infant death certificates in California merged with Office of Statewide Health Planning and Development.

Population: One million California live births (2007-10) after live birth and after pregnancy termination.

Methods: Logistic regression was used to estimate odds ratios (ORs) of PTB of 20-36 weeks of gestation and its subcategories for IPIs after a live birth and after a pregnancy termination. We used conditional logistic regression (two IPIs/mother) to investigate associations within mothers.

Main outcome measure: PTB relative to gestations of ≥ 37 weeks.

Results: Analyses included 971 211 women with IPI after live birth, and 138 405 women with IPI after pregnancy termination with 30.6% and 74.6% having intervals of <18 months, respectively. IPIs of <6 months or 6-11 months after live birth showed increased odds of PTB adjusted ORs for PTB of 1.71 (95% CI 1.65-1.78) and 1.20 (95% CI 1.16-1.24), respectively compared with intervals of 18-23 months. An IPI >36 months (versus 18-23 months) was associated with increased odds for PTB. Short IPI after pregnancy termination showed a decreased OR of 0.87 (95% CI 0.81-0.94). The within-mother analysis showed the association of increased odds of PTB for short IPI, but not for long IPI.

Conclusions: Women with IPI <1 or >3 years after a live birth were at increased odds of PTB-an important group for intervention to reduce PTB. Short IPI after pregnancy termination was associated with reduced odds for PTB and needs to be further explored.

Tweetable abstract: Short and long IPI after live birth, but not after pregnancy termination, showed increased odds for PTB.

Keywords: Interpregnancy interval; preterm birth; prevention; risk assessment.