The association between threatened preterm labour and perinatal outcomes at term: a population-based cohort study

Objective: To estimate the association between threatened preterm labour (TPTL) and perinatal outcomes of infants born at term. Design: A population-based cohort study of perinatal outcomes following TPTL <37 weeks of gestation with delivery at term. Setting: Nova Scotia, Canada. Population: All non-anomalous, singleton pregnancies ≥37 weeks of gestation without antepartum haemorrhage from 1988 to 2019. Methods: Using data from the Nova Scotia Atlee Perinatal Database, TPTL was defined as pregnancies with a hospital admission between 20 and 37 weeks of gestation, with a diagnosis code denoting TPTL with administration of antenatal corticosteroids, or with administration of any tocolysis. Poisson regression models were used to estimate the risk ratios (RR) with 95% CI of maternal and perinatal outcomes in women who had an episode of TPTL relative to those who did not. Main outcome measures: Birthweight for gestational age below the tenth centile and a composite of perinatal mortality or severe perinatal morbidity. Results: Of 256 599 term deliveries meeting the inclusion criteria, 2278 (0.9%) involved TPTL. The risks of the primary outcomes were higher among those with TPTL relative to those without: birthweight for gestational age below the tenth centile (RR 1.24, 95% CI 1.11–1.39) and the composite of perinatal mortality/severe perinatal morbidity (RR 1.33, 95% CI 1.15–1.54). Conclusions: Although the prevalence of TPTL in term deliveries is low, affected pregnancies are at increased risk for adverse perinatal outcomes. Increased fetal surveillance should be considered in the management of pregnancies affected by TPTL.