May 10, 2012 — Elective labor at term gestation (beyond 37 weeks) can reduce perinatal mortality in developed countries when compared with expectant management. This benefit occurs without increasing the risk for operative delivery. There was, however, an increased risk for neonatal admission into the special care unit.
Sarah J. Stock, PhD, from the MRC Centre for Reproductive Health, University of Edinburgh in the United Kingdom, and colleagues presented the results of the retrospective cohort study in an article published online May 10 in the British Medical Journal. Using Scottish birth and death records, they analyzed data for more than 1.2 million women with single pregnancies who gave birth after 37 weeks' gestation between 1981 and 2007. One of the strengths of the study is the use of this unselected population database.
At 40 weeks' gestation, deaths occurred in 37 (0.08%) of 44,764 patients in the induction group compared with 627 (0.18%) of 350,643 patients in the expectant management group (adjusted odds ratio [OR], 0.39; 99% confidence interval [CI], 0.24 - 0.63). Eight percent with induction of labor compared with 7.3% with expectant management were admitted to the neonatal special care unit, however (adjusted OR, 1.14; 99% CI, 1.09 - 1.20).
The characteristics of the elective induction of labor group and the expectant management group were different on univariate analysis. The authors adjusted for these differences in the multivariable analysis. Outcomes were adjusted for age at delivery, parity, year of birth, birth weight, deprivation category, and where appropriate, mode of delivery.
There was no significant difference in spontaneous vertex delivery rates between elective induction of labor and the expectant management groups for weeks 37, 38, and 39. However, primary analysis showed an association of elective induction of labor with a reduction in spontaneous vertex delivery rates compared with the expectant management group at weeks 40 and 41 (adjusted OR, 1.26; 99% CI, 1.22 - 1.31; adjusted OR, 1.55; 99% CI, 1.49 - 1.61, respectively; P < .001 for both comparisons). This difference was maintained for week 41, but not week 40, during secondary analysis (adjusted OR, 1.01; 99% CI, 0.97 - 1.05 at 40 weeks; P = .518; adjusted OR, 1.06; 99% CI, 1.03 - 1.09 at 41 weeks; P < .001).
The authors estimate that for every 1040 women having elective induction of labor at 40 weeks, 1 newborn death may be prevented. This would result, however, in 7 more admissions to a special care baby unit.
Induction of labor is frequently performed for pregnancies of more than 41 weeks' gestation to reduce perinatal mortality. This is the first large study to examine the risks and benefits of induction at term on newborn deaths. It also quantifies the benefits of induction of labor in terms of a reduction in perinatal mortality.
Study limitations include, but are not confined to, potential errors in coding and lack of data about all potential confounding variables (eg, body mass index and place of delivery).
"Although residual confounding may remain," the authors conclude, "our findings indicate that elective induction of labour at term gestation can reduce perinatal mortality in developed countries without increasing the risk of operative delivery."
The study was funded by a research grant from the Chief Scientist Office of the Scottish Government Health Directorate. The authors have disclosed no relevant financial relationships.
BMJ. Published online May 10, 2012. Abstract
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