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Epidemiology

Poster Session 2

(420) CS in Single Cephalic Term Nulliparas: The Changing Size of Robson Group 1 and 2

Tuesday, February 13, 2024
3:30 PM – 5:00 PM  
Location: Prince George's Exhibit Hall CDE, Lower Atrium Level
Objective: To describe the change in sizes, pathway to delivery and and caesarean section (CS) rates in Single Cephalic Nulliparas >=37 weeks’ gestation from 1974 to 2022.

Study Design: This is a single centre longitudinal cohort study at an Irish tertiary maternity centre. The study population was singleton cephalic pregnancies at >=37 weeks’ gestation with spontaneous or induced labour or prelabour caesarean section (Robson Group 1, 2a and 2b) delivered between 1974 and 2022. Regression analysis was performed to analyze trends in the size of each group as proportion of the overall population, and for CS rates within the groups.

Results: From 1974 to 2022, the CS Rate in Single Cephalic Nulliparas >=37 weeks’ gestation (SCNT) increased from 4.5% to 32.3% (115/2575 to 811/2515). Group 1 made up a decreasing proportion of the SCNT from 78.4% (2020/2575) to 39.5% (993/2515) and Group 2 made up an increasing proportion from 21.6% (555/2575) to 60.5% (1522/2515, R-Squared 0.951, p=0.005, Figure 1).  Within Group 1, the CS Rate increased from 2.3% in 1974 to 11.9% in 2022 (R-Squared 0.9644, p=0.003). The CS Rate in Group 2 increased from 12.3% to 45.5% (R-Squared 0.994, p=0.002). Since the first recording of Group 2a and 2b in 2004, , the absolute size of Group 2a increased from 33.0% of the Singleton Cephalic Nulliparous population >=37 weeks gestation to 45.5% (R-Squared=0.829, p< 0.001). The absolute size of 2b also increased from 1.9% to 7.1% of the single cephalic nulliparous population >=37 weeks’ gestation (R-Squared 0.829, p< 0.001).

Conclusion:

Among Single Cephalic Nulliparas >=37 weeks’ gestation, the primary pathway to delivery is now induced labour, where it was once spontaneous labour.  Induced labour is associated with higher rates of CS than spontaneous labour, and CS within both have also increased over the last sixty years. When analysing CS rates in SCNT >=37 weeks’ gestation, examination of the size of Group 1, 2a and 2b is critical as the first step to interpretation.