Induction of Labour for Post Term Pregnancy: An Observational Study

EDITORIAL COMMENT: We accepted this paper for publication because it discusses the important subject of prolonged pregnancy and whether induction of labour is associated with a significant change in the operative delivery rate and the perinatal mortality and morbidity rates. In many centres induction of labour is performed at 41 weeks' gestation in those patients who consent or wish this to be performed and indeed it is often the patient's motivation that determines the induction. Because of this practice the incidence of prolonged pregnancy which is defined as 42 weeks' gestation or beyond, has fallen from approximately 10–12% 30 years ago to about 2% in the 1990's. One of the senior reviewers of this paper provided the following statements which he considered should be kept in mind by readers of this paper. Although this is a carefully conducted study, the results and conclusions need to be interpreted with extreme caution. The words in the title ‘an observational study’ alert the reading audience to pitfalls which could result from systematic differences between the induction and ‘control’ groups which would necessarily be reflected in differences in outcomes which could then (erroneously) be attributed to the intervention. For example, women who declined the offer of induction of labour (who would therefore be ‘controls’) might also decline a recommendation for instrumental delivery which could then be misinterpreted to mean that induction of labour result in a ‘higher’ operative delivery rate compared to controls. A second caveat applies to the practice of multiple analyses of characteristics of 2 populations; 1 of 20 of such comparisons will result in p = 0.05 by chance alone. This point needs to be considered when interpreting findings reported here such as more married than unmarried women having induction of labour performed, or the conflicting finding of a decrease in the Caesarean section rate following induction for multiparas but an increase in nulliparas. These findings, and others, may be due to chance, and cannot in this observational study be viewed with the same confidence as findings derived from a randomized controlled trial. Summary: The aim of the study was to compare the 2 management protocols for postterm pregnancy; elective induction of labour at 42 weeks' gestation and continuing the pregnancy with fetal monitoring while awaiting spontaneous labour. A retrospective observational study compared a cohort of 360 pregnancies where labour was induced with 486 controls. All pregnancies were postterm (>294 days) by an early ultrasound scan. Induction of labour was achieved with either prostaglandin vaginal pessaries or gel or forewater rupture and Syntocinon infusion. The control group consisted of women with postterm pregnancies who were not induced routinely and who usually had twice weekly fetal assessment with cardiotocography and/or ultrasound. Women who had their labour induced differed from those who awaited spontaneous labour. Nulliparas (OR 1.54; 95% CI 1.24–1.83) and married women (OR 1.76; 95% CI 1.45–2.06) were more likely to have their labour induced. There was no association between the type of caregiver and induction of labour. Induction of labour was associated with a reduction in the incidence of normal vaginal delivery (OR 0.63, 95% CI 0.43–0.92) and an increased incidence of operative vaginal delivery (OR 1.46; 95% CI 1.34–2.01). There was no difference in the overall rate of Caesarean section. There was no difference in fetal or neonatal outcomes. Parity had a major influence on delivery outcomes from a policy of induction of labour. Nulliparas in the induced group had worse outcomes with only 43% achieving a normal vaginal delivery (OR 0.78, 95% CI 0.65–0.95). In contrast for multiparas, the induced group had better outcomes with less Caesarean sections (OR 0.88, 95% CI 0.81–0.96). This retrospective observational study of current clinical practice shows that induction of labour for postterm pregnancy appears to be favoured by nulliparous married women. It suggests that induction of labour may improve delivery outcomes for multigrin as but has an adverse effect for nulliparas.