Maternal age and risk of cesarean section in women with induced labor at term - a Nordic register-based study

INTRODUCTION: Over the last decades, induction of labor has increased in many countries along with increasing maternal age. We assessed the effects of maternal age and labor induction on cesarean section at term among nulliparous and multiparous women without previous cesarean section.

MATERIAL AND METHODS: We performed a retrospective national registry-based study from Denmark, Finland, Iceland, Norway, and Sweden including 3 398 586 deliveries between 2000 and 2011. We investigated the impact of age on cesarean section among 196 220 nulliparous and 188 158 multiparous women whose labor was induced, had single cephalic presentation at term, and no previous cesarean section. Confounders comprised country, time-period, and gestational age.

RESULTS: In nulliparous women with induced labor the rate of cesarean section increased from 14.0% in women less than 20 years of age to 39.9% in women 40 years and older. Compared with women aged 25-29 years, the corresponding relative risks were 0.60 (95% confidence interval [95% CI] 0.57 to 0.64) and 1.72 (95% CI 1.66 to 1.79). In multiparous induced women the risk of cesarean section was 3.9% in women less than 20 years rising to 9.1% in women 40 years and older. Compared with women aged 25-29 years, the relative risks were 0.86 (95% CI 0.54 to 1.37) and 1.98 (95% CI 1.84 to 2.12), respectively. There were minimal confounding effects of country, time-period, and gestational age on risk for cesarean section.

CONCLUSIONS: Advanced maternal age is associated with increased risk of cesarean section in women undergoing labor induction with a single cephalic presentation at term without a previous cesarean section. The absolute risk of cesarean section is 3-5 times higher across 5-year age groups in nulliparous relative to multiparous women having induced labor.