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


fourchet, perineal skin, vaginal mucous membrane

does not involve fascia or muscle


as for first degree, plus involves fascia and muscle

does not involve the anal sphincter


as for second degree, plus involves anal sphincter

does not involve extend through the rectal mucosa


as for third degree, plus extends through the rectal mucosa to expose the lumen of the rectum



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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