Perineal lacerations may occur during vaginal delivery of an infant. The significance of the laceration depends on how large it is and what structures have become involved.
Features of a perineal laceration:
(1) degree, based on anatomic involvement
(2) length
Anatomic Extent
Degree
fourchet, perineal skin, vaginal mucous membrane
does not involve fascia or muscle
first
as for first degree, plus involves fascia and muscle
does not involve the anal sphincter
second
as for second degree, plus involves anal sphincter
does not involve extend through the rectal mucosa
third
as for third degree, plus extends through the rectal mucosa to expose the lumen of the rectum
fourth
Tears may also involve the urethra if an adequate episiotomy is not performed.
According to Nager and Helliwell (page 446, Figure 1):
estimated length of the laceration in cm =
= ((length of one lateral side in cm) + (length of second lateral side in cm)) / 2
While this is simple, it does not appear to be geometrically correct for giving the height of a triangle. The simplest equation would be the distance from the apex to the median point of the base.
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