This study examined factors affecting participation in obstetrics among obstetrician–gynecologists and changes in participation over time.

Using physician billings from Ontario, Canada, from 1992/1993 to 2001/2002, the study examined the impact of physician age, gender, practice location, and years of practice on participation in obstetrics with multiple logistic regression and repeated measures analyses. It also examined differences in practice patterns between obstetrics providers and non-providers using linear and log-linear regressions.

Obstetrics participation declined with age, from 96% among physicians under age 35, to 34% among those over age 64 (2001/2002 figures). Regressions demonstrated a lower likelihood of performing obstetrics in successive years (odds ratio [OR] 0.95 per year; 95% confidence interval [CI] 0.93, 0.98) and among physicians who were older (OR 0.91 per year of age; 95% CI 0.90, 0.93), female (OR 0.57; 95% CI 0.36, 0.91), and practising in cities with medical schools (OR 0.58; 95% CI 0.44, 0.78). The crude obstetrics participation rate dropped from 82% to 77%, from 1992/1993 to 2001/2002. The physician age- and sex–adjusted participation rate dropped from 80% in 1992/1993 to 77% in 2001/2002. Obstetrics providers had almost double the annual billings of non-providers ($364,000 versus $187,000; P < .001), and more on-call days worked (105 versus 13; P < .001). Non-providers of obstetrics derived more of their billings from outpatient visits, psychotherapy, and diagnostic tests. The likelihood of an obstetrics non-provider resuming obstetrics was 1.1% per year.

The proportion of obstetrician–gynecologists practising obstetrics declined modestly in the last decade, partly because of more female physicians in the workforce who were less likely to practice obstetrics. Planners should consider these trends when estimating how many obstetrician–gynecologists to train to meet future societal needs.