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Pelvic Floor Birth Injuries: What does the research say?

More than 85% of females who undergo a vaginal birth will sustain some degree of perineal tear, known as a birth related injury. About 0.6–11% of all vaginal deliveries resulting in a third-degree or fourth-degree tear known as an obstetric anal sphincter injury (OASI). Fortunately, we know the incidence of perineal tears decreases with each birth from 90 % having an perineal tear with their first birth to 68.8% having another tear with additional births. This new generation of 30 to 40 year-old-somethings who are giving birth are no longer interested to “wait and see'' what happens during pregnancy and desires to know the risk and rewards of different types of birth.

We were privileged to be a small part of the 10% of American physical therapists who participated in an international conference hosted by the fabulous Taryn Hallam. Taryn is an Australian physiotherapist and research guru. The international cohort opened our eyes to learn that Australia, New Zealand, Ireland, England and our northern neighbors Canada are well ahead and forward thinking about care for pelvic health.

Pelvic Floor Birth Injuries

Preventing pelvic floor muscle injuries, such as obstetric anal sphincter injury (OASI), aka 3rd or 4th degree tears, is one of the most common concerns we see amongst our pregnant/postpartum clients. Besides dealing with perineal pain during the first few weeks of recovery, OASI is also associated with an increased risk of fecal incontinence and there is a very strong correlation between OASI and levator ani (a deep pelvic floor muscle) injury.

Pelvic Muscle Avulsion

A birth injury can also include, a levator ani muscle avulsion occurs when there is a disconnection of the levator ani muscle from its attachment onto the pubic bone. It is reported in about 13-36% of people after a vaginal birth and is known to be an important risk factor for pelvic organ prolapse. The rate of obstetric pelvic floor injury and the consequences of urinary and fecal incontinence and pelvic organ prolapse have increased in recent years. Women are not routinely informed of these risks even though studies have suggested that women want to know their risk of developing pelvic floor dysfunction to help make decisions about child birth and to motivate them to seek out preventative strategies such as Pelvic Floor Physical Therapy. But is the current research concrete enough yet to predict who is more likely to experience pelvic floor muscle trauma? Let’s take a look…

Women are not routinely informed of these risks even though studies have suggested that women want to know their risk of developing pelvic floor dysfunction to help make decisions about child birth and to motivate them to seek out preventative strategies such as Pelvic Floor Physical Therapy.

Risk of OASI and Levator Ani Injury

According to the recent research, the following have been found to increase the risk of OASI and levator ani muscle injury:

Prolonged second stage (or pushing phase) of labor. Prolonged second stage was identified as greater than 90 minutes. It was found that for every 30 minute increase in duration of the second stage, there was a 23% increase in risk of OASI. This may be explained by increased swelling of the tissues, making them more vulnerable to injury. The longer the second stage, the more swelling that occurs around the perineum.

Instrumental delivery, with forceps being more of a risk factor than vacuum. While the use of forceps alone was associated with a higher risk of OASI and levator avulsion, regardless of length of second stage, vacuum assisted deliveries alone were not independently associated with OASI. Only in the event of a prolonged second stage were vacuum assisted deliveries associated with an increased risk of OASI, so it was probably more related to the longer stage of labor than the presence of a vacuum.

Absence of epidural. Epidural analgesia was found to be independently associated with a decrease in OASI rate. It is hypothesized that in the absence of an epidural, the urge to push is felt more powerfully, which could result in a more rapid expulsion of the baby’s head. When the baby’s head is birthed rather quickly, this does not allow the pelvic floor muscles to undergo a more slow and controlled stretch, thus leading to more forces pushing on the perineum

Obstructed labor requiring the use of fundal pressure. Uterine fundal pressure is a maneuver that involves manual pressure to the top of the uterus directed down to the birth canal in an attempt to assist a vaginal birth. This technique is often used in the event of obstructed labor, which is when the baby is having difficulty exiting the pelvis due to a mechanical or physical blockage. The research indicated that the use of uterine fundal pressure significantly increased the risk of levator ani muscle avulsion.

So to summarize so far, obstructed labor leading to either prolonged second stage, need for fundal pressure, or need for instrumental delivery, particularly forceps, substantially increases the risk of both OASI and levator avulsion.

Which begs the question, does prenatal pelvic floor function influence who might be more at risk of an obstructed labor? Can pelvic therapy and pregnancy education minimize the risk of:

Longer second stage = more swelling

Forceps or vacuum assisted labors

Absence of epidural increase urge to push

Obstructed labor due to mechanical blockage

Stay tuned for our upcoming blog to learn more!


To start preparing in less than 2 hours, join Dr. Becca to learn how you can prepare for birth with simple tips on prenatal perineal massage, pelvic positioning during labor to minimize tearing, and how to advocate for your birth story. BONUS- Get moving again postpartum with our 6 week Mindful Movement Strategies!

Dr. Becca Jones, PT, DPT, CSCS, is a 2016 graduate of New York University with her Doctorate of Physical Therapy. Her passion for supporting people through their pregnancy and/or post partum journey inspired her to specialize in pelvic health. Dr. Becca believes in providing holistic, individualized care in order to restore comfort and build confidence to get people back to what they love.

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