Perineal tear

Illustration of two perineal tears.

In obstetrics, a perineal tear is a spontaneous (unintended) laceration of the skin and other soft tissue structures which, in women, separate the vagina from the anus. Perineal tears mainly occur in women as a result of vaginal childbirth, which strains the perineum. Tears vary widely in severity. The majority are superficial and require no treatment, but severe tears can cause significant bleeding, long-term pain or dysfunction. A perineal tear is distinct from an episiotomy, in which the perineum is intentionally incised to facilitate delivery.

Anatomy

In a woman, the anus and the vaginal opening lie within the anatomical region known as the perineum. Each opening is surrounded by a wall, and the anal wall is separated from the vaginal wall by a mass of soft tissue including:

• The muscles of the anus (corrugator cutis ani, the internal anal sphincter and the external anal sphincter)

• The medial muscles of the urogenital region (the superficial transverse perineal muscle, the deep transverse perineal muscle and bulbocavernosus)

• The medial levator ani muscles (puborectalis and pubococcygeus)

• The fascia of perineum, which covers these muscles

• The overlying skin and subcutaneous tissue

A perineal tear may involve some or all of these structures, which normally aid in supporting the pelvic organs and maintaining faecal continence.

Classification

Tears are classified into four categories:

• First-degree tear: laceration is limited to the fourchette and superficial perineal skin or vaginal mucosa
• Second-degree tear: laceration extends beyond fourchette, perineal skin and vaginal mucosa to perineal muscles and fascia, but not the anal sphincter
• Third-degree tear: fourchette, perineal skin, vaginal mucosa, muscles, and anal sphincter are torn; third-degree tears may be further subdivided into three subcategories:
  • 3a: partial tear of the external anal sphincter involving less than 50% thickness
  • 3b: greater than 50% tear of the external anal sphincter
  • 3c: internal sphincter is torn
• Fourth-degree tear: fourchette, perineal skin, vaginal mucosa, muscles, anal sphincter, and rectal mucosa are torn

Cause

In humans and some other primates, the head of the term fetus is so large in comparison to the size of the birth canal that term delivery is rarely possible without some degree of trauma. As the head passes through the pelvis, the soft tissues are stretched and compressed. The risk of severe tear is greatly increased if the fetal head is oriented occiput posterior (face forward), if the mother has not given birth before or if the fetus is large.

Prevention

Several techniques are used to reduce the risk of tearing, but with little evidence for efficacy. Antenatal digital perineal massage is often advocated, and may reduce the risk of trauma only in nulliparous women. ‘Hands on’ techniques employed by midwives, in which the foetal head is guided through the vagina at a controlled rate have been widely advocated, but their efficacy is unclear. Waterbirth and labouring in water are popular for several reasons, and it has been suggested that by softening the perineum they might reduce the rate of tearing. However, this effect has never been clearly demonstrated. The ‘Epi-no birth trainer’, a relatively recent invention, is a device specifically designed to strengthen and stretch the perineum during pregnancy. In spite of some promising studies, systematic review has shown no effect on the rate of tearing or episiotomy.

Prevalence

Over 85% of women having a vaginal birth sustain some form of perineal trauma, and 60-70% receive stitches. A retrospective study of 8603 vaginal deliveries found a third degree tear had been clinically diagnosed in only 50 women (0.6%). However, when the same authors used anal endosonography in a consecutive group of 202 deliveries, there was evidence of third degree tears in 35% of first-time mothers and 44% of mothers with previous children. These numbers are confirmed by other researchers.

Complications

First and second degree tears rarely cause long-term problems. Among women who experience a third or fourth degree tear, 60-80% are asymptomatic after 12 months. Faecal incontinence, faecal urgency, chronic perineal pain and dyspareunia occur in a minority of patients, but may be permanent. The symptoms associated with perineal tear are not always due to the tear itself, since there are often other injuries, such as avulsion of pelvic floor muscles, that are not evident on examination.

Insurance Coverage

A study by the Agency for Healthcare Research and Quality (AHRQ) found that in 2011, first- and second-degree perineal tear was the most common complicating condition for vaginal deliveries in the U.S. among women covered by either private insurance or Medicaid. Second-degree perineal laceration rates were higher for women covered by private insurance than for women covered by Medicaid.