Caesarean birth in women with infertility: population-based cohort study

Objective — Caesarean section (CS) is more common following infertility treatment (IT), but the reasons why remain unclear and confounded. The Robson 10-Group Classification System (TGCS) may further explain variation in CS rates. We assessed the association between mode of conception and CS across Robson groups.

Design — Population-based cohort study.

Setting — Ontario, Canada, in a public healthcare system.

Population — 921,023 births, 2006-2014.

Methods — Modified Poisson regression produced relative risks (RR) and 95% confidence intervals, comparing the risk of CS among women with (i) subfertility without IT, (ii) non-invasive IT (OI, IUI), or (iii) invasive IT (IVF) – each relative to (iv) spontaneous conception (SC).

Main Outcome Measures — CS rate according to one of four modes of conception, overall, and stratified by each of the TGCS groups.

Results — Relative to SC (26.9%), the risk of CS increased in those with subfertility without IT (RR 1.17; 1.16-1.18), non-invasive IT (RR 1.21; 1.18-1.24), and invasive IT (RR 1.39; 1.36-1.42). Within each Robson group, similar patterns of RRs were seen, but with markedly differing rates. For example, in Group 1 (nulliparous, singleton, cephalic at ≥ 37 weeks, with spontaneous labour), the respective rates were 15.0%, 19.4%, 18.7%, and 21.9%. In Group 2 (nulliparous, singleton, cephalic at ≥ 37 weeks, without spontaneous labour), the rates were 35.9%, 44.4%, 43.2%, and 54.1%, while in Group 8 (multiple pregnancy), they were 55.9%, 67.5%, 65.0%, and 69.3%, respectively.

Conclusions — CS is relatively more common in women with subfertility and those receiving IT – an effect that persists across Robson groups.