Gestational age-specific severe maternal morbidity associated with labor induction

Objective: The purpose of this study was to examine the association between labor induction and gestational age-specific severe maternal morbidity.

Study design: Our study was restricted to women who delivered singletons at 37-42 weeks' gestation who had no pregnancy complications from 2003-2010 (n = 1,601,253) in Canada (excluding Quebec). Using a pregnancies-at-risk approach, the week-specific rates of specific morbidity after induction were contrasted with rates among ongoing pregnancies. Logistic regression was used to adjust for confounders.

Results: Induction increased the rate of postpartum hemorrhage that required blood transfusion at 38 weeks' gestation (adjusted rate ratio, 1.28; 95% confidence interval, 1.11-1.49) and 39 weeks' gestation (adjusted rate ratio, 1.21; 95% confidence interval, 1.06-1.38). Induction was also associated with higher rates of pueperal sepsis at 38 and 39 weeks' gestation and venous thromboembolism at 38 weeks' gestation. The absolute increase in morbidity rates was small; the number needed to harm was large (eg, 1270 for postpartum hemorrhage with blood transfusion at 38 weeks' gestation).

Conclusion: Among women without pregnancy complications, induction at earlier term is associated with higher rates of specific severe maternal morbidity, although absolute risks are low.