Objective: To compare associations between interpregnancy intervals (IPIs) and adverse perinatal outcomes in deliveries following IVF with deliveries following spontaneous conception or other (non-IVF) fertility treatments.

Design: Cohort using linked birth certificate and assisted reproductive technology surveillance data from Massachusetts and Michigan.

Setting: Not applicable.

Patient(s): 1,225,718 deliveries.

Intervention(s): None.

Main Outcomes Measure(s): We assessed associations between IPI and preterm birth (PTB), low birth weight (LBW), and small for gestational age (SGA) according to live birth or nonlive pregnancy outcome in the previous pregnancy.

Result(s): In IVF deliveries following previous live birth, risk of PTB was 22.2% for IPI 12 to <24 months (reference); risk of PTB was higher for IPI <12 months (adjusted relative risk [aRR] 1.24, 95% confidence interval [CI] 1.09–1.41) and IPI ≥60 months (aRR 1.12, 95% CI 1.00–1.26). In non-IVF deliveries following live birth, risk of PTB was 6.4% for IPI 12 to <24 months (reference); risk of PTB was higher for IPI <12 and ≥60 months (aRR 1.19, 95% CI 1.16–1.21, for both). In both populations, U-shaped or approximately U-shaped associations were observed for SGA and LBW, although the association of IPI <12 months and SGA was not significant in IVF deliveries. In IVF and non-IVF deliveries following nonlive pregnancy outcome, IPI <12 months was not associated with increased risk of PTB, LBW, or SGA, but IPI ≥60 months was associated with significant increased risk of those outcomes in non-IVF deliveries.

Conclusion(s): Following live births, IPIs <12 or ≥60 months were associated with higher risks of most adverse perinatal outcomes in both IVF and non-IVF deliveries.