A perineal tear, or laceration, is an injury to the skin and muscle between the vaginal opening and the anus that can occur during a vaginal birth. These tears are classified by degree, ranging from a first-degree tear which involves only the skin, to a fourth-degree tear that extends into the anal sphincter and rectum. Many women who experience an intact perineum during their first vaginal delivery may still feel anxious about the possibility of sustaining trauma during a subsequent birth.
The Recurrence Rate After an Intact Perineum
A previous vaginal delivery with an intact perineum or only a minor first-degree tear is a significant protective factor for the second birth. Multiparous women, those who have delivered vaginally before, have a substantially lower overall risk of perineal trauma compared to women giving birth for the first time. The likelihood of a severe tear, specifically a third- or fourth-degree laceration, is greatly reduced following a prior intact perineum.
Studies suggest that a history of an intact perineum can reduce the risk of a severe tear by approximately 91% compared to a first-time mother. While the risk is not completely eliminated, the perineal tissues have already demonstrated the ability to stretch effectively. If a tear does occur in a second birth, it is far more likely to be a minor first- or second-degree laceration that requires simple repair. This reduced risk reflects permanent changes in tissue elasticity and pelvic floor anatomy that occur after the first vaginal passage. However, this protective benefit establishes a lower baseline risk that can still be overridden by specific circumstances during the current labor.
Maternal and Delivery Variables That Influence Risk
Even with the protective history of a previous delivery, certain factors specific to the current pregnancy and labor can increase the risk of tearing. One of the most significant variables is fetal macrosomia, which refers to a birth weight typically greater than 4,000 grams. A larger baby presents a greater diameter to the birth canal, placing increased mechanical stress on the perineal tissues regardless of previous stretching.
The position of the baby during delivery also plays a large role, especially a persistent occiput posterior position, sometimes called “sunny-side up.” In this malposition, the baby’s head is not flexed optimally, which causes a wider diameter of the head to press against the perineum. This can lead to a prolonged second stage of labor, which in itself is associated with an increased risk of severe lacerations.
The need for an instrumental delivery, such as the use of forceps or a vacuum cup, significantly increases the risk of a severe tear. The use of these instruments accelerates the birth process and concentrates pressure on the perineum, which can overwhelm the tissue’s capacity to stretch gradually. Forceps delivery, in particular, has been repeatedly identified as having a higher association with severe trauma.
Labor Techniques to Protect the Perineum
Proactive, evidence-based techniques can be used during pregnancy and labor to further reduce the risk of perineal trauma.
Antenatal Perineal Massage
Antenatal perineal massage, performed regularly starting around 34 to 35 weeks of pregnancy, improves the elasticity of the perineal tissue. Although the benefit is most pronounced for first-time mothers, it can decrease the risk of ongoing perineal pain three months postpartum for women having a second baby.
Warm Compresses
During the second stage of labor, warm compresses applied to the perineum during crowning are a highly effective, low-intervention strategy. The warmth increases blood flow and tissue flexibility, which may reduce the incidence of third- and fourth-degree tears. This technique is typically initiated as the baby’s head begins to distend the perineum.
Birthing Positions
Positions that avoid lying flat on the back are beneficial because they prevent pressure on the tailbone, allowing the pelvic outlet to open more fully. Positions like side-lying or all fours reduce direct tension on the perineum and allow for a more controlled delivery. The side-lying position may increase the likelihood of an intact perineum by preventing excessive strain.
Controlled Pushing
A slow, controlled delivery of the baby’s head is achieved by encouraging spontaneous, or uncoached, pushing rather than directed pushing. Directed pushing (the Valsalva maneuver) involves holding the breath and bearing down forcefully, which can lead to rapid expulsion and sudden trauma. Allowing the natural urge to push gives the perineal tissue sufficient time to stretch around the baby’s head.