Cesarean section rate is a matter of maternal age or parity?

To determine the impact of women's age on the cesarean section (CS) rate according to Robson groups 1, 2A, 3 and 4A.

Retrospective cohort study of term, livebirth, singleton pregnancies with spontaneous or induced labor who delivered at the San Paolo Hospital from 1996 through 2019, and had the Robson group assigned. Women were grouped in 5 age classes (≤24, 25-29, 30-34, 35-39 and ≥40 years). The primary outcome was the rate of CS.

24 843 women were included: 36.4% classified as Robson group 1, 18.9% as Robson group 2A, 34.4% as Robson group 3 and 10.2% as Robson group 4A. The CS rate of women in Robson groups 1, 2A, 3 and 4A was 6.6%, 21.8%, 1.6% and 4.3% respectively. In nulliparous women [Robson groups 1 and 2A] group 1, the adjusted OR of CS increased steadily from 30 to ≥40 years, when compared to women aged 25-29 years. On the contrary, in multiparous women [Robson groups 3 and 4A] significant increased OR were present only for women ≥40 years. In young women [≤24 years] there was a significant reduction in the number of cesarean sections only in Robson group 1.

The results of our study show that multiparous women aged ≥40, either in spontaneous or induced labor have an independent twofold increased risk of delivering by cesarean section when compared to women of 25-29 years. On the contrary, in nulliparous women, the risk slightly, but significantly, increases with age and again becomes twofold in women ≥40 years.