International comparisons of preterm birth: higher rates of late preterm birth are associated with lower rates of stillbirth and neonatal death

Abstract

Objective: To examine international rates of preterm birth and potential associations with stillbirths and neonatal deaths at late preterm and term gestation.

Design: Ecological study.

Setting: Canada, USA and 26 countries in Europe.

Population: All deliveries in 2004.

Methods: Information on preterm birth (<37, 32-36, 28-31 and 24-27 weeks of gestation) and perinatal deaths was obtained for 28 countries. Data sources included files and publications from Statistics Canada, the EURO-PERISTAT project and the National Center for Health Statistics. Pearson correlation coefficients and random-intercept Poisson regression were used to examine the association between preterm birth rates and gestational age-specific stillbirth and neonatal death rates. Rate ratios with 95% confidence intervals were estimated after adjustment for maternal age, parity and multiple births.

Main outcome measures: Stillbirths and neonatal deaths ≥ 32 and ≥ 37 weeks of gestation.

Results: International rates of preterm birth (<37 weeks) ranged between 5.3 and 11.4 per 100 live births. Preterm birth rates at 32-36 weeks were inversely associated with stillbirths at ≥ 32 weeks (adjusted rate ratio 0.94, 95% CI 0.92-0.96) and ≥ 37 weeks (adjusted rate ratio 0.88, 95% CI 0.85-0.91) of gestation and inversely associated with neonatal deaths at ≥ 32 weeks (adjusted rate ratio 0.88, 95% CI 0.85-0.91) and ≥ 37 weeks (adjusted rate ratio 0.82, 95% CI 0.78-0.86) of gestation.

Conclusions: Countries with high rates of preterm birth at 32-36 weeks of gestation have lower stillbirth and neonatal death rates at and beyond 32 weeks of gestation. Contemporary rates of preterm birth are indicators of both perinatal health and obstetric care services.