Using inter-institutional practice variation to understand the risks and benefits of routine labour induction at 41(+0) weeks

Abstract

Objective: To evaluate the risks and benefits of routine labour induction at 41(+0) weeks' gestation for mother and newborn.

Design: Population-based retrospective cohort study of inter-institutional variation in labour induction practices for women at or beyond 41(+0) weeks' gestation.

Population: Women in British Columbia, Canada, who remained pregnant ≥41(+0) weeks and delivered at one of the province's 42 hospitals with >50 annual deliveries, 2008-2012 (n = 14,627).

Methods: The proportion of women remaining pregnant a week or more past the expected delivery date who were induced at 41(+0) or 41(+1) weeks' gestation for an indication of 'post-dates' was calculated for each institution. We used instrumental variable analysis (using the institutional rate of labour induction at 41(+0) weeks as the instrument) to estimate the effect of labour induction on maternal and neonatal health outcomes.

Main outcome measures: Caesarean delivery, instrumental delivery, post-partum haemorrhage, 3rd or 4th degree lacerations, macrosomia, neonatal intensive care unit admission, and 5-minute Apgar score <7.

Results: Institutional rates of labour induction at 41(+0) weeks ranged from 14.3 to 46%. Institutions with higher (≥30%) and average (20-29.9%) induction rates did not have significantly different rates of caesarean delivery, instrumental delivery, or other maternal or neonatal outcomes than institutions with lower induction rates (<20%). Instrumental variable analyses also demonstrated no significantly increased (or decreased) risk of caesarean delivery (0.69 excess cases per 100 pregnancies [95% CI -10.1, 11.5]), instrumental delivery (8.9 per 100 [95% CI -2.3, 20.2]), or other maternal or neonatal outcomes in women who were induced (versus not induced).

Conclusions: Within the current range of clinical practice, there was no evidence that differential use of routine induction at 41(+0) weeks affected maternal or neonatal health outcomes.

Keywords: Caesarean delivery; instrumental variable; labour induction; post-dates; prolonged pregnancy.