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Objectives: We sought to determine the rates of obstetrical anal sphincter tears (OASIS) between types of obstetrical care providers at Kingston General Hospital (KGH) and in Ontario via the Better Outcomes Registry Network (BORN).

Methods: This cross-sectional study collected patient, demographic, and delivery data from all vaginal deliveries at KGH from June 2011 to June 2014 and all vaginal deliveries through the BORN database from June 2012 to June 2014.

Results: During this period, 4.6% and 3.5% of all vaginal deliveries at KGH and in Ontario, respectively, were complicated by OASIS. The OASIS’ rates were not statistically different between admitting care providers at KGH: 4.9%, 3.8%, and 3.7% of vaginal deliveries by obstetricians, family physicians, and midwives, respectively, in contrast to a higher rate of OASIS in women admitted under midwifery care in the province-wide data: 3.4%, 3.2%, and 4.4% for obstetricians, family physicians, and midwives, respectively. The rate of OASIS in patients who had an intrapartum transfer of care (TOC) from a family physician or midwife to an obstetrician was 13.8% at KGH, and 13.6% as reported by BORN, significantly higher than 3.8% (KGH) or 2.9% (BORN) in those who remained under the family physician, or midwife. The relative risk of OASIS in women transferred to an obstetrician compared to those who were admitted and delivered by an obstetrician was 3.9 (95% confidence interval, 3.6-4.3, P < 0.0001).

Conclusions: Only when an intrapartum TOC is needed does the OASIS rate substantially increase, reflecting the underlying indication for TOC is leading to more intervention associated with risk of OASIS.