Biological determinants of spontaneous late preterm and early term birth: a retrospective cohort study.

Objective Our aim was to examine the association between biological determinants of preterm birth (infection and inflammation, placental ischaemia and other hypoxia, diabetes mellitus, other) and spontaneous late preterm (34–36 weeks) and early term (37–38 weeks) birth. Design Retrospective cohort study. Setting City of London and Middlesex County, Canada. Sample Singleton live births, delivered at 34–41 weeks to London-Middlesex mothers following spontaneous labour. Methods Data were obtained from a city-wide perinatal database on births between 2002 and 2011 (n = 17 678). Multivariable analyses used multinomial logistic regression. Main outcome measure The outcome of interest was the occurrence of late preterm (34–36 weeks) and early term (37–38 weeks) birth, compared with full term birth (39–41 weeks). Results After controlling for covariates, there were associations between infection and inflammation and late preterm birth (aOR = 2.07, 95% CI 1.65, 2.60); between placental ischaemia and other hypoxia and late preterm (aOR = 2.21, 95% CI 1.88, 2.61) and early term (aOR = 1.25, 95% CI 1.13, 1.39) birth; between diabetes mellitus and late preterm (aOR = 3.89, 95% CI 2.90, 5.21) and early term (aOR = 2.66, 95% CI 2.19, 3.23) birth; and between other biological determinants (polyhydramnios, oligohydramnios) and late preterm (aOR = 2.81, 95% CI 1.70, 4.64) and early term (aOR = 1.89, 95% CI 1.32, 2.70) birth. Conclusions Our findings show that delivery following spontaneous labour even close to full term may be a result of pathological processes. Because these biological determinants of preterm birth contribute to an adverse intrauterine environment, they have important implications for fetal and neonatal health.