Maternal age and elective cesarean section in a low-risk population.

Objective: To examine the association between maternal age and elective cesarean section in primiparous and para one women in a low-risk population.

Design: Population-based registry study.

Setting: Norway.

Population: The source population was all mothers giving birth to their first or second child from 1 January 1999 to 31 December 2006. The final study population comprised 229 370 primiparous and para one low-risk mothers.

Methods: Data were extracted from the Medical Birth Registry of Norway. We constructed a low-risk population by excluding pregnancies with medical conditions associated with elective cesarean section and maternal age. The association between maternal age and elective cesarean was analysed by relative-risk models.

Main Outcome Measures: Elective cesarean section.

Results: In this low-risk population, the proportion of cesarean section was 9%, and 27% of these were elective. Cesarean delivery increased substantially with increasing maternal age, especially elective cesarean section. In primipara, elective cesarean section increased from 0.6 to 7.5% of all deliveries, corresponding to a relative risk of 11.7 (95% confidence interval 8.9-15.4) in women ≥ 40 years relative to 20-24 years. When comparing women ≥ 40 years with those aged below 25 years, the relative risk in para one without previous cesarean section was 4.5 (95% confidence interval 3.5-5.8; the proportion increasing from 1.4 to 6.2%), while in para one with previous cesarean section it was 2.9 (95% confidence interval 2.4-3.6; the proportion increasing from 17.5 to 51.5%).

Conclusions: We found a close association between maternal age and elective cesarean section in a low-risk population.