Predictors of mode of birth and duration of labour following induction using prostaglandin vaginal gel.

BACKGROUND AND AIMS: Using data from a randomised controlled trial (RCT) comparing two policies of prostaglandin (PGE2) vaginal gel induction of labour (IOL) at term, this study aimed to determine: (i) demographic/clinical factors that predict IOL outcomes; and (ii) clinical characteristic(s) of women who would benefit from a policy of amniotomy once technically possible as opposed to giving more PGE2.

MATERIAL AND METHODS: Following an initial PGE2 dose, women were randomised to amniotomy or repeat-PGE2. Using RCT data, two multivariate models were developed, assessing the relationship between demographic/clinical characteristics and the outcomes of caesarean section (CS), and vaginal delivery within 24 h (VD < 24 h). Regression-equations were used to predict the likelihood of CS and VD < 24 h, varying independent predictors from the multivariate analyses.

RESULTS: Of 245 term women undergoing IOL, 90 had a CS, 155 delivered vaginally and 79 had a VD < 24 h. Controlling for confounders, nulliparity [adjusted odds ratio (aOR) = 3.71 (1.55, 8.88)] and modified Bishop's score (MBS) at first review [aOR = 0.78 (0.66, 0.92)] were independently associated with CS. Nulliparity [aOR = 0.06 (0.02, 0.15)], MBS at first review [aOR = 1.66 (1.35, 2.05)], and a policy of early amniotomy [aOR = 2.28 (1.04, 5.00)] were associated with VD < 24 h. Modelling using regression equations, and varying both MBS at first review and parity, there was no scenario where repeat PGE2 was predicted to be superior to an earlier amniotomy.

CONCLUSIONS: Following IOL using PGE2 vaginal gel at term, both parity and cervical favourability at first review are associated with CS and VD < 24 h. All combinations of parity and MBS at first review predicted fewer CS and greater likelihood of VD < 24 h with a policy of amniotomy once technically possible.