(HealthDay) -- Narrow-angled episiotomies increase the risk of obstetric anal sphincter injuries (OASIS), while other factors, including point of incision and episiotomy length and depth, reduce the risk of OASIS, according to a study published online March 6 in BJOG: An International Journal of Obstetrics & Gynaecology.
Mona Stedenfeldt, of the University Hospital of North Norway in Tromsø, and colleagues conducted a case-control study of 74 women with a history of a single vaginal birth and an episiotomy. The researchers identified, photographed, and measured the episiotomy scar in 37 women with OASIS and 37 controls.
The researchers found that, for each 5.5-mm increase in episiotomy depth there was a 70 percent decrease in the risk of sustaining OASIS (odds ratio [OR], 0.30); for each 4.5-mm increase in the distance from the midline to the incision point of the episiotomy there was a 56 percent decreased risk (OR, 0.44); and for each 5.5-mm increase in episiotomy length there was a 75 percent decrease in the risk of sustaining OASIS (OR, 0.25). The mean angle did not differ between the groups, but a "U-shaped" association was seen between angle and OASIS (OR, 2.09), with an angle either smaller than 15 degrees or greater than 60 degrees associated with an increased risk (OR, 9.00).
"The present study showed that scarred episiotomies with depth >16 mm, length >17 mm, incision point >9 mm lateral of midpoint and angle range 30 to 60 degrees are significantly associated with less risk of OASIS," the authors write.
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