
Am Fam Physician. 2021;103(12):745-752
Published online: April 19, 2021.
†Deceased
Author disclosure: No relevant financial affiliations.
Obstetric lacerations are a common complication of vaginal delivery. Lacerations can lead to chronic pain and urinary and fecal incontinence. Perineal lacerations are defined by the depth of musculature involved, with fourth-degree lacerations disrupting the anal sphincter and the underlying rectal mucosa and first-degree lacerations having no perineal muscle involvement. Late third-trimester perineal massage can reduce lacerations in primiparous women; perineal support and massage and warm compresses during the second stage of labor can reduce anal sphincter injury. Conservative care of minor hemostatic first- and second-degree lacerations without anatomic distortion reduces pain, analgesia use, and dyspareunia. Minor hemostatic lesions with anatomic disruption can be repaired with surgical glue. Second-degree lacerations are best repaired with a single continuous suture. Lacerations involving the anal sphincter complex require additional expertise, exposure, and lighting; transfer to an operating room should be considered. Limited evidence suggests similar results from overlapping and end-to-end external sphincter repairs. Postdelivery care should focus on controlling pain, preventing constipation, and monitoring for urinary retention. Acetaminophen and nonsteroidal anti-inflammatory drugs should be administered as needed. Opiates should be avoided to decrease risk of constipation; need for opiates suggests infection or problem with the repair. Osmotic laxative use leads to earlier bowel movements and less pain during the first bowel movement. Simulation models are recommended for surgical technique instruction and maintenance, especially for third- and fourth-degree repairs.

Grading of Lacerations

FIRST- AND SECOND-DEGREE LACERATIONS
First-degree lacerations involve only the perineal skin without extending into the musculature.1 Second-degree lacerations involve the perineal muscles without affecting the anal sphincter complex.
THIRD-DEGREE LACERATIONS

Degree | Description |
---|---|
First | Laceration of perineal skin only |
Second | Laceration involving the perineal muscles but not involving the anal sphincter |
Third | Laceration involving the anal sphincter muscles
|
Fourth | Laceration involving the anal sphincter complex and rectal epithelium |
The majority of obstetric anal sphincter injuries are third-degree lacerations that involve the anal sphincter complex without disrupting the rectal mucosa.1 The anal sphincter complex comprises the larger external anal sphincter containing striated muscle and a distinct capsule plus the small internal anal sphincter of involuntary smooth muscle that often cannot be identified.
FOURTH-DEGREE LACERATIONS
Fourth-degree lacerations are the most severe, involving the rectal mucosa and the anal sphincter complex.1 Disruption of the fragile internal anal sphincter routinely leads to epithelial injury. Fourth-degree lacerations occur in less than 0.5% of patients.1 Figure 2 shows a fourth-degree perineal laceration.

Prevention of Obstetric Lacerations
BEFORE DELIVERY
A Cochrane review demonstrated that digital perineal self-massage starting at 35 weeks' gestation reduces the rate of perineal lacerations in primiparous women with a number needed to treat of 15 to prevent one laceration.5 Because the review included fewer than 2,500 patients, reductions could not be demonstrated for specific laceration grades. Women reported that self-massage was initially uncomfortable, unpleasant, and even painful, but nearly 90% would recommend the technique to others.6
DURING DELIVERY
Studies of prevention during delivery have focused on prevention of obstetric anal sphincter injuries. Most risk factors involve labor management, including labor induction, labor augmentation, use of epidural anesthesia, delivery with persistent occipitoposterior positioning, and operative vaginal deliveries7 (Table 21,8,9). Although epidural anesthesia increases risk of obstetric anal sphincter injuries through increased operative vaginal delivery, epidural use reduces lacerations overall.10

Fetal risk factors |
Large fetal weight (> 4,000 g [8 lb, 13.1 oz]) |
Occipitotransverse or occipitoposterior position at delivery |
Intrapartum risk factors |
Delivery in lithotomy position |
Epidural anesthesia (increases risk of severe lacerations, decreases overall lacerations) |
Midline episiotomy |
Operative vaginal delivery (i.e., forceps, vacuum) |
Oxytocin use |
Prolonged second stage of labor (> 60 minutes) |
Maternal risk factors |
20 years or younger |
Asian ethnicity9 |
Nulliparity |
Vaginal birth after cesarean delivery |
Several labor techniques can reduce anal sphincter injuries. During the second stage of labor, perineal massage and application of a warm compress to the perineum are beneficial.11 Perineal support during delivery, variably described as squeezing the lateral perineal tissue with the first and second fingers of one hand to lower pressure in the middle posterior perineum while the other hand slows the delivery of the fetal head, reduces obstetric anal sphincter injuries, with a number needed to treat of 37 in a systematic review.12,13
Routine episiotomy does not reduce anal sphincter lacerations and is not recommended.14 Mediolateral episiotomy is not protective for obstetric anal sphincter injuries, and midline episiotomy increases the risk.9 Neither delaying maternal pushing following full cervical dilation nor altering birthing position reduces obstetric anal sphincter injuries.15,16
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