Before childbirth there were no instances of asymmetry of the pubovisceral muscle, and we did not observe appearances suggestive of avulsion of the muscle from the pelvic sidewall. In the 39 women delivered vaginally, levator avulsion was diagnosed in 14 (36%, 95% confidence interval 21-51%) cases. Defects were on the left (n = 8), on the right (n = 4) or bilateral (n = 2). There was no association between subjectively judged pelvic floor contraction strength and avulsion defects.
There were significant or nonsignificant associations with higher maternal age among those delivered vaginally (P = .1 on t test) and with vaginal operative delivery (P = .07 on Fisher exact test) and worsened or de novo stress incontinence postpartum (4/36 without defects, 6/14 with defects, P = .02 on Fisher exact test). When this analysis was undertaken for the entire cohort of 50 women, defects were significantly associated with maternal age (P = .03), while the association with worsened or de novo stress incontinence became nonsignificant (P = .09). Other obstetric factors, eg, birth weight, were not associated with defects. The increase in bladder neck descent as shown in Table 2 was more marked in those women who showed avulsion defects (+ 7.8 mm compared with + 20 mm, P = .001 on t test). No defects were seen in those 11 women delivered abdominally, and there was no significant increase in bladder neck descent in those women either.
According to a search of MEDLINE (any language; 1966 to 3rd week of June 2005; keywords [used singly and in any possible combination]: “pubovisceral,” “levator,” “puborectalis,” “pelvic floor,” “child birth,” “delivery,” “trauma,” “birth”), this is the first study in the world literature to demonstrate a direct association between soft tissue trauma to the levator ani and vaginal childbirth. Such a study has become possible as a result of recent advances in diagnostic ultrasound, with 3-dimensional and 4-dimensional volume ultrasound giving access to the axial plane.12 This technology allows imaging of the inferior aspects of the levator ani, enabling us to observe functional anatomy in any operator-defined plane, and in real time. It has been shown that the assessment of hiatal dimensions2 and of major morphological abnormalities is highly reproducible, the latter with a kappa of 0.825 (95% confidence interval 0.59–1) in unpublished data.
The incidence of avulsion defects in women delivered vaginally was surprisingly high at approximately 1 of 3. This is clearly higher than the prevalence of such defects in parous women as imaged by magnetic resonance and 3-dimensional ultrasound. Of 160 primiparous women of approximately 30 years of age, 29 (18%) showed defects of the pubovisceral portion of the levator ani in an observational MRI study from Michigan.9 No such defects were observed in 80 nulliparas. A larger study on 338 women undergoing urodynamic assessment and 3-dimensional pelvic floor ultrasound (mean age 52.8 years) demonstrated a prevalence of avulsion defects of 15.4% in parous women, with none seen in nulliparas (Steensma A, Dietz HP. What is the clinical relevance of major defects of the levator ani muscle? [abstract] Int Urogynecol J 2005;16:S76). Both those prevalence figures are outside the confidence interval for the proportion estimate derived from our data (21–51%).
The difference in prevalence between ultrasound and MRI data could be due to differences in imaging methodologies, but it is harder to explain the discrepancy between studies conducted using the same ultrasound methodology. One explanation may be variations in obstetric practice and demographic developments. It has recently been shown that age at delivery is a strong predictor of future stress urinary incontinence, and the average age at first delivery in this study was rather high at 31 years. This is much higher than for women seen in a pelvic floor clinic today (23.6 years in a subset of the study quoted above). One wonders whether the continuing rise in women’s age at first delivery may result in a higher likelihood of pelvic floor trauma such as demonstrated in this study.
As regards obstetric factors, this study clearly did not have the power to investigate delivery-related risk factors for avulsion injury to the levator ani. There was only a nonsignificant association between such defects and vaginal operative delivery and none at all between defects and length of second stage. It is evident that such injuries may occur as a consequence of outwardly normal, uncomplicated deliveries—the shortest second stage among women who suffered an avulsion injury was only 33 minutes, although 6 of 14 had a prolonged second stage over 2 hours.
At the moment there is little information on the clinical significance of the soft tissue trauma documented in this and other studies. While childbirth is associated with pelvic organ prolapse and incontinence in epidemiological studies (see Dietz and Schierlitz14 for a review of current evidence), it is by no means clear whether this is due to delivery-related direct levator trauma. In this study there was a weakly significant association between avulsion injury and worsened or de novo stress incontinence postpartum (P = .02), but it is likely that large cross-sectional studied with decade-long follow-up will be required to fully investigate this issue. Own data suggests that avulsion injury of the levator muscle is associated with prolapse of the anterior and central compartment rather than with bladder dysfunction, and this would agree well with the fact that the etiological role of childbirth is much more strongly established for pelvic organ prolapse than for stress incontinence.14
Quite independent of such considerations, the possibility of a changing prevalence of pelvic floor trauma due to demographic developments is particularly intriguing. Women who showed an avulsion after vaginal delivery were older than those without, although this difference did only reach statistical significance when the whole population, including cesarean deliveries, was considered. We know that older age at first delivery is a risk factor for operative delivery, whether vaginal or abdominal.15,16 It is possible that older age at first delivery may be a risk factor for pelvic floor trauma, a hypothesis that is supported by recent epidemiological data from Norway. Rortveit et al showed in a reanalysis of the EPINCONT study that stress incontinence was more likely in women who had had their first baby at an older age (Rortveit G, Hunskaar S. The association between the age at the first and last delivery and urinary incontinence [meeting abstract]. Neurourol Urodyn 2004;23:562-3).
As the age of primiparae in Western societies has risen by about ten years over the last two generations, such observations may have significant public health implications. In addition, women are not just older when they have their first babies, mean birthweight has also been increasing steadily-and in some studies birthweight is another risk factor for pelvic floor damage17 and urogenital prolapse.18 The current obesity epidemic may further exacerbate such trends. We may well be facing a long-term increase in pelvic floor morbidity due to changing demographics.
In conclusion, this study found that vaginal delivery can cause morphological alterations visible on 3-dimensional pelvic floor imaging. Avulsion of the pubovisceral muscle off the pelvic sidewall is common and can be visualized easily using 3-dimensional and 4-dimensional translabial pelvic floor ultrasound. The clinical significance of such trauma however remains to be established.
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© 2005 by The American College of Obstetricians and Gynecologists. Published by Wolters Kluwer Health, Inc. All rights reserved.
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