The risk of having a premature baby is lowest when pregnancies are spaced 2 to 2.5 years apart; it increases if women get pregnant again too soon or wait more than eight years.
Evidence from Studies
No evidence studies found yet.
What Would Prove This
Per GRADE and EBM methodology, here is what ideal scientific evidence would look like to definitively prove or disprove this claim, ordered from strongest to weakest.
A systematic review of RCTs could confirm whether both short and long IPIs causally increase preterm birth risk, establishing the U-shape as a causal phenomenon.
A systematic review of randomized trials assigning women to conceive at 6 months, 24–29 months, or 72 months postpartum, with preterm birth as the primary outcome and adjustment for maternal age, fertility status, and prior complications.
An RCT could determine whether both short and long IPIs independently increase preterm birth risk compared to moderate intervals.
A multicenter RCT assigning 6,000 women to conceive at 6 months, 24–29 months, or 72 months postpartum, with preterm birth before 37 weeks as the primary outcome, and adjustment for maternal age, BMI, and prior preterm birth history.
A prospective cohort could confirm the U-shaped association by measuring IPI and preterm birth across a wide range of intervals while adjusting for confounders.
A prospective cohort of 20,000 women from diverse backgrounds, tracking IPI from delivery to next conception and monitoring for preterm birth, with monthly assessments of health, nutrition, and socioeconomic factors.
A case-control study could compare IPI distributions across the full spectrum to confirm the U-shaped risk curve.
A matched case-control study of 3,000 preterm births and 6,000 term births, stratified by IPI categories (<6, 6–23, 24–29, 30–59, 60–96, >96 months), matched for maternal age, race, and prior preterm history.
A cross-sectional survey could estimate the prevalence of preterm birth across IPI ranges in a population.
A national cross-sectional survey of 100,000 women with two or more births, asking about timing of prior births and outcomes, with preterm birth confirmed by medical records.