What Is a Fourth-Degree Tear During Childbirth?

A fourth-degree tear is the most severe form of perineal injury that can occur during vaginal childbirth. It extends from the vaginal tissue through the perineal muscles, through the entire anal sphincter complex, and into the lining of the rectum itself. This distinguishes it from the more common first- and second-degree tears, which affect only the skin and perineal muscles, and from third-degree tears, which involve the anal sphincter but stop short of the rectal lining. Fourth-degree tears are uncommon, but they carry real consequences for bowel control, sexual function, and emotional well-being that can persist for years if not managed well.

How the Grading System Works

Perineal tears during childbirth are classified into four degrees based on what structures are damaged. A first-degree tear involves only the vaginal skin or perineal skin. A second-degree tear goes deeper into the perineal muscles but does not reach the anal sphincter. A third-degree tear extends into the anal sphincter itself, and is further subdivided: 3a involves less than half the thickness of the external sphincter, 3b involves more than half of the external sphincter, and 3c involves the internal anal sphincter as well. A fourth-degree tear includes everything in a 3c tear and additionally tears through the rectal mucosa, the inner lining of the rectum. This means there is a direct communication between the vaginal wound and the inside of the bowel, which is why repair is more complex and the stakes are higher.

Third- and fourth-degree tears are sometimes grouped together under the term “obstetric anal sphincter injuries,” or OASIS. This grouping reflects the fact that any tear reaching the anal sphincter raises concerns about future bowel control. But fourth-degree tears carry a distinctly worse prognosis than third-degree tears, so the distinction matters clinically.

What Raises the Risk

Certain factors make severe tearing more likely, and researchers have studied these extensively. Having your first baby is one of the strongest risk factors. A large study at a tertiary center found that first-time mothers had roughly three and a half times the odds of sustaining a severe tear compared with women who had given birth before.¹ Baby size matters too: heavier babies, particularly those over four kilograms, consistently show up as a risk factor across studies.²

The baby’s position during delivery plays a major role. When the baby comes through facing the mother’s front rather than her back, a position called occiput posterior, the risk of severe tearing rises sharply. In one retrospective study, two-thirds of women who sustained OASIS had a baby in this position.³ Shoulder dystocia, where the baby’s shoulder gets stuck behind the pubic bone after the head has emerged, also increases the risk.

Instrumental delivery is another important factor. Forceps carry a substantially higher risk of severe tears than vacuum extraction. One study found that forceps use was associated with more than four times the odds of severe tearing, while vacuum was considerably lower.⁴ Midline episiotomy, where the surgical cut is made straight down toward the anus rather than at an angle, has long been recognized as increasing the risk.⁵ Mediolateral episiotomy, the angled cut, is generally considered safer in this regard, though it comes with its own trade-offs. Other factors that have been linked to severe tears include induction of labor, a prolonged second stage of pushing, obesity, post-term delivery beyond 40 weeks, and the lithotomy position during delivery.²

Why Some Tears Get Missed

One of the underappreciated problems with severe perineal tears is that they can be misdiagnosed or missed entirely. If the birth attendant does not perform a thorough examination of the rectum after delivery, an injury to the sphincter or rectal lining may go unrecognized. Anal sphincter injuries and isolated rectal tears can be missed if a complete examination is not performed, leading to serious consequences including anal incontinence. Research on digital rectal examination, the standard bedside check, shows that it catches less than half of anal sphincter injuries, with one study reporting a sensitivity of about 44%.⁶ That means more than half of injuries may not be identified by finger exam alone.

This diagnostic gap is a real problem. A tear that goes unrepaired is far more likely to lead to chronic bowel symptoms than one caught and fixed at the time of delivery. Missed injuries are also a significant source of medicolegal claims, making accurate identification a priority in obstetric training and protocols.

How a Fourth-Degree Tear Is Repaired

Repair should happen in the operating room or a well-equipped delivery suite, under regional or general anesthesia. The repair proceeds in layers, starting with the deepest damage and working outward. The torn rectal lining is sutured first, then the internal anal sphincter, then the external anal sphincter, and finally the perineal muscles and skin.

For the external sphincter, surgeons use one of two approaches. The overlapping technique involves taking the two torn ends of the muscle and overlapping them in the midline, stitching them together so the muscle wraps around the anal canal. The end-to-end technique simply brings the torn edges directly back together with mattress stitches.⁷ There has been ongoing debate about which is better. A Cochrane review found fewer symptoms of fecal urgency and incontinence at one year with the overlapping method, but a randomized trial following women for three years found no lasting difference between the two approaches.⁸ In that trial, end-to-end repair actually showed lower rates of flatal incontinence at one year, but the gap narrowed by year two and was negligible by year three. Most expert centers today are comfortable with either technique, choosing based on the specific anatomy of the tear.

After the repair, antibiotics and stool softeners are standard.⁹ Keeping stools soft in the first weeks is not optional. Hard stools put pressure on fresh suture lines and can cause the repair to break down. Pain management, adequate hydration, and a fiber-rich diet are the practical cornerstones of the early recovery period.

Checking the Repair With Ultrasound

Endoanal ultrasound after repair can reveal whether the sphincter muscles have been successfully brought back together. In one study, imaging performed just days after primary repair found that 90% of women had detectable defects in the sphincter on ultrasound, suggesting that even a “good” repair often leaves some structural imperfection.¹⁰ Women with fourth-degree tears and other major injuries were more likely to have combined defects in both the internal and external sphincter, and those combined defects were associated with worse bowel symptoms and lower anal canal pressures.¹¹ Ultrasound after repair helps guide follow-up decisions, including whether to recommend a cesarean section in a future pregnancy.

Long-Term Bowel Control

The question that weighs most heavily on women who experience a fourth-degree tear is whether they will regain full bowel control. The honest answer is that most women do recover meaningful function, but a significant minority deal with some degree of anal incontinence long term. A network meta-analysis found that the average incidence of anal incontinence among women who sustained a fourth-degree tear was about 29%, compared with roughly 22% for the least severe third-degree tears.¹² Fourth-degree tears carried more than twice the odds of incontinence compared with 3a tears.

A large study focusing specifically on the difference between third- and fourth-degree tears found even starker numbers over the longer term. Nearly 59% of women with a fourth-degree tear in their first delivery reported anal incontinence at follow-up, compared with 41% of those with a third-degree tear. For fecal incontinence specifically, meaning involuntary loss of stool rather than just gas, the rates were about 31% versus 15%.¹³ These differences persisted even after accounting for other factors like baby weight and mode of delivery, confirming that the grade of the tear itself matters. It is worth noting that “anal incontinence” in these studies often includes involuntary gas, which is far more common than loss of solid stool. The term sounds alarming, and for some women the symptoms are genuinely life-altering, but for others the issue is limited to occasional difficulty controlling gas.

Pelvic floor rehabilitation after repair can improve outcomes. In a follow-up study of women who underwent pelvic floor exercises after surgical repair of third- and fourth-degree tears, about one in five reported anal incontinence at one month postpartum. By one year, with continued rehabilitation, none reported fecal incontinence and only about 7% still experienced some flatus incontinence.¹⁴ Electrical stimulation was tried as well but was abandoned in that study due to anal pain.

Effects on Sexual Function

Sexual health after a severe perineal tear is a topic that many women feel uncomfortable raising with their providers, but the data shows it deserves attention. A prospective study of first-time mothers found that 53% of women with third- or fourth-degree tears reported painful intercourse at 12 months postpartum, compared with 25% of women who had no tear or only a minor one.¹⁵ Women with severe tears had roughly twice the risk of dyspareunia compared with women who had minimal or no tearing. Another study found that women with severe tears showed significant decreases across multiple domains of sexual function, including desire, arousal, lubrication, orgasm, and satisfaction, at one year after delivery.¹⁶

Beyond pain during intercourse, women with severe tears were more likely to report constipation, urinary incontinence, and urinary leakage after delivery, and to have a more negative attitude toward future pregnancy.¹⁷ These cascading effects on quality of life are part of what makes fourth-degree tears more than just a surgical problem.

The Emotional Toll

The psychological impact of a severe tear is increasingly recognized in the research literature but still underappreciated in clinical practice. Women who experienced perineal trauma were more likely to report post-traumatic stress symptoms, and each additional physical symptom was associated with substantially increased odds of adverse psychological outcomes.¹⁸ A longitudinal study found that women who sustained OASIS were more likely to experience their birth as traumatic and reported more avoidance symptoms of post-traumatic stress, along with a greater negative impact on parenting tasks. These symptoms persisted at six to ten months postpartum.¹⁹

Avoidance symptoms are particularly insidious. A woman who avoids thinking about the birth, avoids physical intimacy, or avoids seeking medical follow-up for ongoing symptoms is likely to see those problems compound. Recognizing this pattern early and offering psychological support alongside physical rehabilitation is something maternity services are slowly getting better at, but there is still a long way to go.

Rectovaginal Fistula

The most feared complication specific to fourth-degree tears is a rectovaginal fistula, an abnormal connection between the rectum and the vagina that allows gas or stool to pass through the vaginal canal. This happens when the primary repair fails to heal properly. In one study of 61 women with fourth-degree tears, five developed a rectovaginal fistula, a rate of about 8%.²⁰ The study identified forceps delivery and mediolateral episiotomy as independently associated with fistula formation, possibly because irregular lacerations after an angled episiotomy are harder to suture evenly, leading to areas of poor blood flow, ischemia, and eventual tissue breakdown. A fistula typically requires additional surgery to correct and can profoundly affect quality of life in the interim.

What Happens in a Subsequent Pregnancy

Women who have had a severe tear face a real decision about how to deliver their next baby. The recurrence risk is not trivial. A large cohort study found that among women who had a third- or fourth-degree tear at their first birth and went on to deliver vaginally a second time, 7.2% sustained another severe tear, compared with 1.3% of women who had no prior tear. That five-fold increase in risk is significant.²¹ The rate of elective cesarean at the second birth was about 24% among women with a prior severe tear, compared with 1.5% in those without.

For fourth-degree tears specifically, the conversation about future deliveries is more weighted toward cesarean. One study found that based on clinical guidelines, only about 7% of women who had sustained a fourth-degree tear would not be offered a cesarean section for their next delivery; those were the women who were entirely asymptomatic with normal ultrasound and muscle function testing.²² In practice, there is considerable variation among obstetricians in how they counsel women after a severe tear. Some lean more readily toward cesarean; others support vaginal delivery with close monitoring.²³ If you have had a fourth-degree tear and are considering another pregnancy, expect a detailed conversation that weighs your current symptoms, your ultrasound findings, and your own preferences.

Can Severe Tears Be Prevented

No strategy eliminates the risk entirely, but several approaches reduce it. Warm compresses applied to the perineum during the second stage of labor have shown promise. Randomized controlled trials have found that warm compresses reduce the incidence of severe perineal tears and also reduce pain during pushing.²⁴²⁵ The mechanism is probably a combination of improved tissue elasticity from the heat and relaxation of the pelvic floor muscles.

Beyond warm compresses, the hands-on perineal support technique, where the birth attendant actively supports the perineum during crowning and controls the speed of the baby’s head delivery, is widely recommended. Avoiding midline episiotomy in favor of mediolateral episiotomy when a cut is necessary reduces the risk of the incision extending into the sphincter. Choosing vacuum extraction over forceps when instrumental delivery is needed also helps, as forceps consistently carry a higher risk of severe tears.⁵ Allowing the baby’s head to deliver slowly and in a controlled manner, rather than rushing the expulsive phase, is another practical step. Prenatal perineal massage starting around 34 weeks of pregnancy is also commonly recommended, though the evidence for it specifically preventing fourth-degree tears is less robust than the evidence for reducing less severe tears.

The Financial and Systemic Costs

The burden of severe tears extends beyond individual patients. In the United Kingdom, the economic cost of obstetric anal sphincter injuries was estimated between £3.7 million and £9.8 million across 2013 and 2014, depending on whether the injuries occurred during assisted or spontaneous delivery. In the United States, complications related to perineal trauma cost roughly $83 million between 2007 and 2011.²⁶ These figures include surgical repair, extended hospital stays, follow-up care, treatment for incontinence, and medicolegal costs. Litigation related to OASIS is a recognized concern in obstetric practice, particularly in cases where injuries were missed at the time of delivery or where preventive steps were not taken during high-risk deliveries. Investing in better training for perineal assessment, wider adoption of prevention bundles like warm compresses and perineal support, and access to specialist follow-up clinics is, by the numbers, cheaper than dealing with the downstream consequences.