What Happens to Your Pelvic Floor During Birth?
Vaginal delivery is a predictor of pelvic floor dysfunction after birth, including pelvic organ prolapse, urinary incontinence, and chronic pelvic pain. Accompanying this, vaginal delivery is related to perineal and anal sphincter injury. So, what happens to the pelvic floor muscles and surrounding structures during vaginal birth?
During delivery, resistance to the descending fetus can come from the bony pelvis, the pelvic floor muscles, and the cervix. During active labour, the pelvic floor muscles and surrounding nerves undergo physiological stretch, which can result in injury. Not surprisingly, there is a direct relationship between the length of labour and the degree of birth-related trauma, likely related to prolonged stretch of these structures(1). It has been observed that pelvic floor muscle contraction during labour increases this resistance, supporting the notion that hypertonicity in the pelvic floor muscles from over-training can lead to more resistance as the baby descends through the pelvic canal, which can prolong labour(1).
With the associated muscle stretch, the pelvic floor muscles are at risk of injury, particularly the medial pubococcygeus, iliococcygeus, and puborectalis muscles. The branches of the pudendal nerve are also at risk of stretch-induced injury, especially those that innervate the anal sphincter. In a study that used three-dimensional computer-based simulation to study pudendal nerve stretch during birth, they saw a 33% stretch in the perineal nerve branches that innervate the anal sphincter, where 25% is the established threshold for permanent peripheral nerve damage(2).
“It has been observed that pelvic floor muscle contraction increases this resistance, supporting the notion that hypertonicity in the pelvic floor muscles from over-training can lead to more resistance as the baby descends through the pelvic canal, which can prolong labour.”
Knowing that these muscles and nerves undergo stretch and strain during birth, it is important to take steps towards minimizing resistance from the pelvic floor muscles to the descending fetal head. Pelvic floor muscle training and education provided by a licenced Pelvic Floor Physiotherapist can assist you in learning how to relax your pelvic floor muscles, how to get comfortable with feeling stretch in the perineal tissues, which positions will minimize resistance from the pelvic floor muscles and pelvic girdle, and exercises to improve mobility in the pelvis and hips to optimize positioning and release muscle tension that can contribute to a tight pelvic floor.
Overall, the pelvic floor muscles and associated nerves undergo stretch during delivery that puts these structures at risk of stretch-related obstetric injury. The perineum and anal sphincter are also at risk of tearing during labour and delivery. Individuals who had unplanned caesarean births and previously attempted to deliver vaginally with a prolonged labour are at risk of these same injuries. Injuries to the pelvic floor, perineum, and nervous structures can prohibit the pelvic floor from carrying out important functions, including pelvic organ support and sphincteric activity that controls continence, as well as induce chronic pain that can lead to postpartum sexual dysfunction.
It is recommended that expecting clients seek Pelvic Floor Physiotherapy prepartum to prepare for delivery in order to minimize risk of injury, as well as after birth to improve recovery outcomes.
References
Serati, Maurizio & Bogani, Giorgio. (2016). A Computerized Model of Pelvic Floor Muscles Physiology During Delivery. 10.1007/978-3-319-18197-4_3.
Lien KC, Morgan DM, Delancey JO, Ashton-Miller JA (2005) Pudendal nerve stretch during vaginal birth: a 3D computer simulation. Am J Obstet Gynecol 192:1669–1676
