Maternal, fetal, and placental conditions associated with medically indicated late preterm and early term delivery: a retrospective study

ObjectiveOur objectives were: (1) to examine the association between maternal, fetal, and placental phenotypes of preterm delivery and medically indicated early delivery of singletons during the late preterm and early term periods; and (2) to identify the specific maternal, fetal, and placental conditions associated with these early deliveries. DesignRetrospective study. SettingCity of London and Middlesex County, Ontario, Canada. SampleSingleton live deliveries, at 34-41weeks of gestation to women in London and Middlesex. MethodsWe obtained data from a city-wide perinatal database (2002-2011; n=25699). We used multinomial logistic regression for multivariable analyses. Main outcome measureThe outcome was the occurrence of medically indicated late preterm (34-36weeks of gestation) and early term (37-38weeks of gestation) delivery, versus delivery at full term (39-41weeks of gestation). ResultsAfter controlling for confounding factors, all phenotypes were associated with increased odds of medically indicated late preterm and early term delivery. Within the maternal phenotype, chronic maternal medical conditions were associated with increased odds of medically indicated early term delivery (e.g. for gastrointestinal disease, adjusted odds ratio, aOR1.72, 95%CI 1.47-2.00; for anaemia, aOR1.40, 95%CI 1.20-1.63), but not late preterm delivery. ConclusionsThe aetiology of medically indicated early delivery close to full term is heterogeneous. Patterns of associations suggest slightly different conditions underlying the late preterm and early term phenotypes, with chronic maternal medical conditions being associated with early term delivery but not with late preterm delivery. These results have implications for the prevention of early delivery as well as the identification of high-risk groups among those born early.