Perineal and vaginal lacerations are common, affecting as many as 79% of vaginal deliveries, and can cause bleeding, infection, chronic pain, sexual dysfunction, and urinary and fecal incontinence.^1,2

Grading of Lacerations

Criteria from the American College of Obstetricians and Gynecologists (ACOG) help determine repair techniques and estimate prognosis.¹ Figure 1 shows the muscles affected by perineal 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

Approximately 3% of lacerations involve clinically evident obstetric anal sphincter injuries, doubling the risk of fecal incontinence at five years postpartum.^3,4 These lacerations are further classified by the extent of anal sphincter injury (Table 1).¹

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 2^1,8,9). Although epidural anesthesia increases risk of obstetric anal sphincter injuries through increased operative vaginal delivery, epidural use reduces lacerations overall.¹⁰

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