Phenotypic Classification of preterm Birth Among Multiparous Women: A Population-Based Cohort Study.

OBJECTIVE: The Global Alliance to Prevent Prematurity and Stillbirth developed a phenotypic classification for preterm birth using clinical presentation (rather than risk factors) to improve surveillance. The objective of this study was to determine distributions of preterm birth phenotypes and associations with Caesarean section, low Apgar score, and neonatal death in multiparous women, stratifying by first versus recurrent preterm births.

METHODS: This population-based cohort study used the Better Outcomes Registry and Network (BORN) of multiparous women giving birth in hospital with a singleton after 20 weeks in Ontario from 2012 to 2014 (Canadian Task Force Classification II-2).

RESULTS: In multiparous women with preterm birth, 29.6% had a history of recurrence, of whom 66.2% had at least one clinical condition associated with the phenotypic model, compared with 63.5% of first preterm births. In recurrent preterm births, criteria for maternal, fetal, and placental conditions were met in 44.5%, 37.9%, and 8.2%, respectively, compared with 36.8%, 39.0%, and 10.4%, respectively, of first preterm births. Associations of preterm birth with Caesarean section, low Apgar score, and neonatal death varied across clinical conditions but were similar between first and recurrent preterm births; for example, for recurrent preterm birth, Caesarean section for maternal, fetal, and placental conditions had odds ratios of 1.66 (95% confidence interval [CI] 1.32-2.07), 1.09 (95% CI 0.80-1.49), and 3.92 (95% CI 1.98-7.78), compared with first preterm birth odds ratios of 1.21 (95% CI 1.03-1.41), 0.92 (95% CI 0.77-1.10), and 6.24 (95% CI 4.07-9.56).

CONCLUSION: This study provides novel evidence of the utility of the preterm birth phenotypic classification model by using stratification for previous preterm birth, a robust predictor-with variation in phenotypes in initial and recurrent preterm births.