Quote:
Originally Posted by orthodoc
You mean length, I think, rather than depth - it has to be full thickness or it's useless, but you don't want it any longer than necessary. (Trust me, you don't want it at all!) 
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I'm considering that both length and depth are important considerations:
"
The present study showed that scarred episiotomies with depth > 16 mm, length > 17 mm, incision point > 9 mm lateral of midpoint and angle range 30–60° are significantly associated with less risk of OASIS. Shrinkage of tissue must be considered."
"The odds ratio estimates show that
there is a 70% reduced risk (OR 0.30, 95% CI 0.14–0.66) of sustaining an anal obstetric sphincter rupture
for each 5.5-mm increase in depth of the episiotomy. In addition, by increasing the distance from the posterior fourchette to the incision point of the episiotomy by 4.5 mm the risk for an obstetric anal injury decreases by 56% (OR 0.44, 95% CI 0.23–0.86).
Also, there is a 75% reduced risk (OR 0.25, 95% CI 0.10–0.61) of obstetric anal injuries
for each 5.5-mm increase in the length of the episiotomy, and there is an increased risk of sustaining such an injury when the angle is either <15 or >60° (OR 9.0, 95% CI 1.1–71.0)."
"This case–control study demonstrated that point of incision, length and depth as well as angle are all parameters associated with anal sphincter injury. Incisions very close to the posterior fourchette,
short episiotomies, angles smaller than 15° or larger than 60° and short depth
are factors that increase the risk of third-degree and fourth-degree perineal tears."
"Further,
depth and episiotomy length were the most significant characteristics associated with less risk of OASIS when compared with incision point. Our findings might indicate that
to unload the perineum sufficiently the episiotomy must obtain a certain length and depth."