[1] Univ Calgary, Dept Obstet & Gynecol, Calgary, AB, Canada
[2] Richmond Rd Diagnost & Treatment Ctr, Calgary Chron Pain Ctr, Calgary, AB, Canada
[3] Ctr Hosp Univ Montreal, Dept Obstet & Gynecol, Montreal, PQ, Canada
[4] Providence Healthcare, Dept Anesthesia, Vancouver, BC, Canada
[5] Univ British Columbia, Dept Anesthesiol Pharmacol & Therapeut, Vancouver, BC, Canada