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

ObjectiveOur 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 (34-36weeks) and early term (37-38weeks) birth. DesignRetrospective cohort study. SettingCity of London and Middlesex County, Canada. SampleSingleton live births, delivered at 34-41weeks to London-Middlesex mothers following spontaneous labour. MethodsData were obtained from a city-wide perinatal database on births between 2002 and 2011 (n=17678). Multivariable analyses used multinomial logistic regression. Main outcome measureThe outcome of interest was the occurrence of late preterm (34-36weeks) and early term (37-38weeks) birth, compared with full term birth (39-41weeks). ResultsAfter 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. ConclusionsOur 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.