Induction of labour in nulliparous women with an unfavourable cervix
Article first published online: 10 MAY 2010
© 2010 The Authors Journal compilation © RCOG 2010 BJOG An International Journal of Obstetrics and Gynaecology
BJOG: An International Journal of Obstetrics & Gynaecology
Volume 117, Issue 7, pages 892–893, June 2010
How to Cite
Pennell, C., Henderson, J. and Dickinson, J. (2010), Induction of labour in nulliparous women with an unfavourable cervix. BJOG: An International Journal of Obstetrics & Gynaecology, 117: 892–893. doi: 10.1111/j.1471-0528.2010.02557.x
- Issue published online: 10 MAY 2010
- Article first published online: 10 MAY 2010
- Accepted 22 February 2010.
We welcome the comments on our randomised controlled trial of induction of labour in nulliparous women with an unfavourable cervix1 and acknowledge the comments regarding the sample size.
As Jozwiak et al.2 observed, the sample size calculation was based on published findings of an observational study by Atad et al.3 This study, which was conducted on a mixed cohort of 250 nulliparous and parous women, found an overall caesarean section rate of 16%. We agree with Jozwiak et al.2 that induction of labour in nulliparous women is more challenging than in parous women, often resulting in higher caesarean section rates. We acknowledge that a sample size of 330, based on a caesarean section rate of 15%, may have been underestimated. The overall caesarean section rate in our study was 39% and the differences in caesarean section rate between study groups did not reach statistical significance. However, our data suggest that caesarean section rates were higher in the double-balloon arm than the other interventions. Further, the duration from induction to delivery was significantly longer with the double-balloon than the single-balloon catheter arm and prostaglandin E2 (PGE2). Therefore, our conclusions were unlikely to have been influenced by this issue.
Further, we acknowledge the authors’ concerns that small improvements in blood gas distributions, although statistically significant, are unlikely to be clinically relevant and that asphyxia is a more important outcome. As such, we reported1 that the proportion of neonates with cord arterial pH values <7.10 was higher in the PGE2 group (n = 8, 7.1%) than the single-balloon group (n = 3, 2.7%). Moreover, four of the five instances of severe neonatal acidaemia (pH < 7.0 and/or base excess less than −12 mmol/l) occurred in the PGE2 arm of the study with one neonate with a base excess less than −12 mmol/l in the double-balloon arm of the study and no women had severe acidosis after cervical ripening with a Foley catheter. We chose to present these data so that future research can include fetal acid–base status and asphyxia as end points after induction of labour. It should be noted that universal cord gas measurement is undertaken routinely within our institution and that this was not just part of our randomised controlled trial. In a population that now amounts to more than 30 000 consecutive deliveries, the proportion of infants born with clinically significant asphyxia (pH <7.0 and base excess less than −12 mmol/l) is very low (0.37%), suggesting that the sample size required to investigate this endpoint would be prohibitive.