Muscle Damage During Childbirth Linked to Pelvic Organ Prolapse

Laurie Barclay, MD

February 05, 2007

February 5, 2007 — Levator ani muscle damage during childbirth has been linked to pelvic organ prolapse and fallen bladder, according to the results of a study reported in the January issue of Obstetrics & Gynecology.

"Potential for pelvic floor injury during vaginal birth is a major factor driving the current debate for prelabor Cesarean delivery on maternal request," write John O. L. DeLancey, MD, from the University of Michigan in Ann Arbor, and colleagues. "Efforts to identify women at high risk are hindered by a lack of understanding regarding how vaginal birth or specific determinants such as levator ani injury lead to prolapse. If the type and mechanism of birth-induced injury could be identified, prevention strategies could be developed to target high-risk women and to avoid subjecting lower-risk women to unnecessary intervention."

This case-control study compared levator ani structure and function in 151 women with prolapse (cases) and 135 women with normal support (controls) determined by pelvic organ prolapse quantification examination. Groups were matched for age, race, and hysterectomy status. Based on magnetic resonance imaging, the investigators determined whether there were "major" (more than half of the muscle missing), "minor" (less than half of the muscle missing), or no defects in the levator ani muscles. An instrumented vaginal speculum measured vaginal closure force at rest and during maximal pelvic muscle contraction.

Compared with control subjects, cases were more likely to have major levator ani defects (55% vs 16%; adjusted odds ratio [OR], 7.3; 95% confidence interval [CI], 3.9 - 13.6; P < .001) but equally likely to have minor defects (16% vs 22%). Of women who reported delivery by forceps, 53% had major defects compared with 28% for women delivered without forceps (adjusted OR, 3.4; 95% CI, 1.95 - 5.78).

Compared with control subjects, women with prolapse generated less vaginal closure force during pelvic muscle contraction (2.0 vs 3.2 Newtons; P < .001). Those with defects generated less force than did women without defects (2.0 vs 3.1 Newtons; P < .001). The genital hiatus was 50% longer in cases than in controls (4.7 ± 1.4 cm vs 3.1 ± 1.0 cm; P < .001).

"Women with prolapse more often have defects in the levator ani and generate less vaginal closure force during a maximal contraction than controls," the authors write.

Study limitations include possible recall bias, case-control study design precluding estimation of the prevalence of levator ani damage among all women, selection bias, exclusion of women from the control group if the vagina or cervix was within a centimeter of the hymen, inability to match groups for parity, and limitations of available assessments of pelvic floor characteristics.

"The high prevalence of prolapse, frequent recurrence after surgery, and the great impact of vaginal birth all indicate the need for further research into the cause and prevention of this distressing condition," the authors conclude. "The findings of this study, by objectively demonstrating levator ani muscle injury and reduced muscle strength in women with prolapse, are important contributions to this field. Future research is needed to both prevent and treat these injuries to reduce the rate of pelvic organ prolapse later in life."

The National Institute of Child Health and Human Development supported this study.

Obstet Gynecol. 2007;109:295-302.

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