411 Predicting caesarean section risk following induction of labour: a pooled analysis of PROBAAT trials

Abstract

Up to 45% of Induction of labour (IOL) end with caesarean section (CS). Currently, the Bishop Score is a widely used prognostic tool for vaginal delivery but conversely, little is known about risk factors for CS following IOL. We aimed to assess maternal and fetal characteristics that influence likelihood of CS following IOL. A secondary analysis of pooled data from PROBAAT I, M, P and II trials. Co-primary outcomes were CS for failure to progress (FTP) or CS for suspected fetal compromise (SFC). Restricted cubic spline was used to explore non-linear relationships. Optimal cut-offs for non-linear patterns were determined with maximised Area Under the Curve. Adjusted odds ratios were computed with logistic regression using multiple imputed (m=30) dataset. Among a total of 2990 women, 540 had a CS, 313 for FTP and 227 for SFC. Regarding the risk of CS for FTP, women aged 30-35 were at elevated risk (aOR 2.32, 95% CI 1.15-1.99) compared with younger women. Nulliparous women had higher risk than multiparous women (aOR 8.07, CI 5.34-12.18). Incremental BMI increased the risk (aOR 1.06, CI 1.04-1.08). Higher birthweight percentile, using 20-49.9% as reference, was also a risk factor for CS due to FTP (for 80-89.9%, aOR 2.66, CI 2.71-4.07; for ≥90% aOR 4.08, CI 2.75-6.05). For CS due to SFC, incremental maternal age (aOR 1.09, CI 1.05-1.12) and BMI (aOR 1.05, CI 1.03-1.08) are associated with increased risk. Compared with multiparous women, nulliparous women had increased risk (aOR 5.91, CI 3.76-9.28). Low birthweight percentile (<10%) carried significantly higher risk for CS due to SFC (aOR 1.93, CI 1.22-3.05) compared to those in the 20-49.9% . Maternal age, BMI, parity, and birthweight percentile are strong predictors of CS following IOL both for FTP and SFC. These characteristics should be considered in combination with Bishop score to stratify risk of failure for women who are undergoing IOL.