Predictive Factors for Delivery within 7 Days after Successful 48-Hour Treatment of Threatened Preterm Labor

Abstract

Objective The aim of this study was to assess which characteristics and results of vaginal examination are predictive for delivery within 7 days, in women with threatened preterm labor after initial treatment. Study Design A secondary analysis of a randomized controlled trial on maintenance nifedipine includes women who remained undelivered after threatened preterm labor for 48 hours. We developed one model for women with premature prelabor rupture of membranes (PPROM) and one without PPROM. The predictors were identified by backward selection. We assessed calibration and discrimination and used bootstrapping techniques to correct for potential overfitting. Results For women with PPROM (model 1), nulliparity, history of preterm birth, and vaginal bleeding were included in the multivariable analysis. For women without PPROM (model 2), maternal age, vaginal bleeding, cervical length, and fetal fibronectin (fFN) status were in the multivariable analysis. Discriminative capability was moderate to good (c-statistic 0.68; 95% confidence interval [CI] 0.60-0.77 for model 1 and 0.89; 95% CI, 0.84-0.93 for model 2). Conclusion PPROM and vaginal bleeding in the current pregnancy are relevant predictive factors in all women, as are maternal age, cervical length, and fFN in women without PPROM and nulliparity, history of preterm birth in women with PPROM.

Keywords: maintenance tocolysis; predictive factors; preterm delivery.

Fig. 1

Trial profile of the APOSTEL-II trial (Assessment of Perinatal Outcome with Sustained Tocolysis in Early Labor).

Fig. 2

(a) Calibration plot of model 1 (women with PPROM) with the observed risk of delivery within 7 days by predicted probabilities of delivery within 7 days. The dots indicate the deciles with 95% confidence intervals of women with similar predicted risk. The histograms indicate the frequencies across the predicted probabilities. (b) Calibration plot of model 2 (women without PPROM) with the observed risk of delivery within 7 days by predicted probabilities of delivery within 7 days. The dots indicate the deciles with 95% confidence intervals of women with similar predicted risk. The histograms indicate the frequencies across the predicted probabilities.