[Physician Comment] Long-term pelvic muscle strength reduced after vaginal childbirth, forceps delivery

Image: PD

From study author Victoria L. Handa MD MHS FACOG, Professor of Obstetrics and Gynecology and Director of the Advanced Training Program in Female Pelvic Medicine and Reconstructive Surgery at Johns Hopkins University*:

“In prior research, we demonstrated that pelvic floor disorders including incontinence and pelvic organ prolapse were significantly more common among women who delivered by vaginal versus cesarean birth.  We also demonstrated that pelvic floor disorders were strongly associated with forceps delivery. However, the biological mechanisms underlying these associations are unknown. In the present study, we test the hypothesis that vaginal childbirth is associated with pelvic muscle weakness, the rationale being that pelvic muscle weakness is thought to contribute to the development of pelvic floor disorders. It has never before been shown that pelvic muscle weakness is a risk factor for the development of pelvic floor disorders.

Our results reveal long-term differences in pelvic muscle strength between women who have experienced vaginal birth and those who have delivered by cesarean. While these findings do not prove that delivery mode causes subsequent changes in pelvic muscle function, we speculate that impairment of pelvic muscle function may be a critical factor underlying the observed association between mode of delivery and pelvic floor disorders.”
*Other authors include Sarah Friedman, Joan Blomquist, Joann Nugent, Kelly McDermott and Alvaro Munoz.

Key study points:

1. The present work is the first to assess the impact of childbirth on long-term pelvic muscle strength and function.

2. Pelvic muscle strength was reduced after vaginal and forceps-assisted vaginal childbirth as compared to Cesarean delivery. In women with a history of vaginal delivery, reduced pelvic muscle strength was associated with pelvic organ prolapse and anal incontinence.

Primer: The pelvic floor, also known as the pelvic diaphragm, is a group of muscles that serve as a sling or hammock across the female pelvis, separating the pelvis from the perineum (image, 1). The pelvic floor, composed of the levator ani complex, coccygei muscles and connective tissue, serves three principle functions:

1. Supports pelvic viscera: serves as the base of the abdomen supporting the bladder, intestines and uterus
2. Maintain continence: houses neurovascular bundles and muscles that control urinary and anal sphincters
3. Facilitate childbirth: resists presenting fetal part, promoting fetal forward rotation through the pelvic girdle (2).

Current literature demonstrates that pregnancy and childbirth are associated with disorders of the pelvic floor. The pathophysiology of pelvic floor disorders is presumed related to the disruption or denervation of the muscles and connective tissue of the pelvic floor caused by compression, stretching or tearing occurring during pregnancy and delivery. Studies show that vaginal delivery is strongly associated with urinary incontinence and pelvic organ prolapse. Midline episiotomies and operative vaginal deliveries increase the risk of sphincter tears (in the levator ani muscle complex) and increase the risk for anal incontinence (3).

However, most studies evaluating the association of childbirth with pelvic floor dysfunction have suffered from short and incomplete follow-up, precluding substantive conclusions that could inform practice. As such, no studies have produced adequate evidence to recommend preventative measures, such as preventative pelvic floor exercises during pregnancy or guide obstetrical management. Currently ACOG recommends against Cesarean delivery to prevent pelvic floor disorders (Grade 2C) (2).

The present work is the first to assess the impact of childbirth (stratified by type and route of delivery) on long-term (6-11 years post-delivery) pelvic muscle strength and function.

Background reading: 

1. Netter images: female pelvic floor

2. Up-to-date: pelvic floor disorders following pregnancy

This [prospective cohort] study is a supplemental study of the Mothers’ Outcomes after Delivery study, a prospective study of pelvic floor outcomes. Researchers measured pelvic muscle strength in 666 eligible women remote from childbirth (6-11 years after delivery). Pelvic muscle strength was measured using a perineometer and obstetric exposures were determined by review of hospital records. Pelvic floor outcomes assessed included stress incontinence, anal incontinence, symptoms of prolapse (via validated questionnaire) and signs of prolapse (via pelvic organ prolapse quanitifaction system).

Peak pelvic muscle strength was reduced in women who delivered vaginally (39cm H2O) as compared to those with exclusively Cesarean deliveries (29cm H2O; P<0.001). Pelvic muscle strength was further reduced after forceps delivery (17cm H2O, P<0.001). Duration of pelvic muscle strength was also reduced in women with remote history of vaginal delivery.

Reduced pelvic muscle strength was associated with symptoms of anal incontinence (p= 0.028) and pelvic organ prolapse (p=0.025) in women after vaginal delivery but not in women after exclusive Cesarean delivery.

In sum: Pelvic muscle strength 6-11 years after childbirth is reduced by vaginal birth and further reduced by forceps delivery. The results of this study suggest that secondary prevention of pelvic floor disorders may be accomplished by targeting women with a history of vaginal birth.

Click to read this article in the Current Issue of Obstetrics & Gynecology

Written by [LH]

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