Understanding caesarean delivery in women with subfertility and infertility treatment using the Robson classification: a population-based cohort study

Objectives Caesarean section rates (CSR) are higher in infertility treatment (IT) pregnancies compared to spontaneous conceptions (SC). We assess the association between mode of conception and CSR in Ontario using the Robson Classification. Methods We conducted a population-based cohort study of deliveries from 2006-2014. Exposures were SC; subfertility (infertility consult without IT); non-invasive IT (OI, IUI); and invasive IT (IVF, ICSI). Deliveries were classified into Robson groups based on parity, previous caesarean section (CS), gestational age, onset of labour, fetal presentation, and number of fetuses. CSR were calculated overall and by Robson group. Modified risk ratios (RR) were reported for the association between exposure and CSR. Results In 921,023 deliveries, CSR were 26.9% with SC, 36.3% with subfertility, 38.8% with non-invasive IT, and 50.6% with invasive IT. Compared to SC, the risk of CS rose by IT invasiveness; with a RR of 1.38 (95% CI 1.36-1.42) in invasive IT. In non-invasive IT, Group 2 (nulliparous, singleton, cephalic, > 36 weeks) and Group 8 (multiple pregnancy) made the largest contribution to CSR at 22.5% and 19.8%. In invasive IT, Group 8 made the largest contribution to CSR at 34.9%. Compared to SC, Robson Groups 3 or 4 (multiparous, singleton, cephalic, > 36 weeks, without a previous CS) with invasive IT had the highest risk of a CS. Conclusions Multiple pregnancy contributes the most to CSR in women with IT. The increased risk of CS in multiparous women with subfertility or IT with no history of a previous CS should be studied.