When to induce labor for post-term? A study of induction at 41 weeks versus 42 weeks.

Objective: To evaluate the pregnancy outcomes of two policies of timing of induction of labor for post-term pregnancies.

Study Design: It is a retrospective study in a University obstetric unit from 1997 to 2002. Five thousand eight hundred and ninety-two singleton, cephalic pregnancies with gestational age at delivery at or more than 41 completed weeks were studied. They were divided into two groups. Group A included women who delivered from January 1997 to February 1999 when the policy of the department was to induce labor for post-maturity at 42 weeks of gestation. Group B included those delivered between March 1999 and December 2002 when the timing of induction for post-term was advanced to 41 weeks. The intrapartum characteristics, delivery and perinatal outcomes were analyzed by Student's t-test and Chi-square test for continuous and categorical variables, respectively.

Results: Two thousand one hundred and seventy-six women were studied in Group A and 3716 in Group B. Twenty-nine percent of these pregnancies in Group A required induction of labor whereas 20.3% were for post-term. In Group B, 58% of pregnancies had labor induction and 55% for post-maturity. For the pregnancies undergoing induction of labor for post-term, both the duration of labor (P<0.001) and the need of intrapartum epidural analgesia were increased (OR 1.3, 95% CI: 1.0-1.6) in Group B. However, there was no significant difference in the mode of delivery, apgar scores and stillbirths between the two study periods.

Conclusion: Compared to routine induction at 42 weeks, induction at 41 weeks is associated with a significantly higher risk of use of medical interventions and associated complications, with no observable benefits.