Phenotypic Classification of Preterm Birth Among Nulliparous Women: A Population-Based Cohort Study

Abstract Objective A classification model based on preterm birth clinical presentations (phenotypes) was proposed at the International Conference on Prematurity and Stillbirth, with calls for validation. This study sought to determine the distribution of clinical phenotypes of preterm birth among nulliparous women, their corresponding associations with maternal characteristics, and the odds ratios (ORs) of preterm Caesarean section and other adverse outcomes. Methods A population-based cohort study was performed of all nulliparous women with singleton pregnancies (>20 weeks) who gave birth in a hospital in Ontario between 2012 and 2014. Logistic regression models were used to estimate adjusted ORs (Canadian Task Force classification II-2). Results Among 113 942 nulliparous women, 6.1% were delivered at Conclusion Approximately two thirds of nulliparous preterm births were grouped into distinct clinical phenotypes. This study demonstrated that outcomes varied across phenotypes, thus providing evidence of benefit for the phenotypic classification model.