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Logo of nihpaAbout Author manuscriptsSubmit a manuscriptHHS Public Access; Author Manuscript; Accepted for publication in peer reviewed journal;
 
Am J Obstet Gynecol. Author manuscript; available in PMC 2010 November 1.
Published in final edited form as:
PMCID: PMC2783527
NIHMSID: NIHMS139249

PELVIC STRUCTURE AND FUNCTION AT 1 MONTH COMPARED TO 7 MONTHS BY DYNAMIC MAGNETIC RESONANCE AFTER VAGINAL BIRTH

Abstract

Objectives

To determine if changes exist in location and movement of pelvic floor structures at one and seven months postpartum.

Study Design

Mid-sagittal MR images from 13 primiparous women with birth events associated with levator ani damage at early (~ 1 month) and late (~ 7 months) postpartum time-points were analyzed. Pelvic floor structures locations at rest and displacements from rest to maximum Kegel and Valsalva were determined. Urogenital and levator hiatus diameters were measured as well.

Results

The perineal body was 7.1 mm and anal verge 7.9 mm higher at seven months postpartum (p = 0.003). Both the urogenital and levator hiatus diameters were smaller at seven months (p < 0.05). Displacement during Kegel and Valsalva was similar between the two time-points.

Conclusion

Resting locations of the perineal body and anal verge are higher at seven months postpartum, but the amount of movement during Kegel or Valsalva does not change.

Keywords: Levator ani, pelvic organ prolapse, pelvimetry, vaginal delivery

Introduction

It is well known that pelvic floor disorders are associated with vaginal delivery.1-3 Several hypotheses have been suggested to explain this association including neural damage, connective tissue changes, anal sphincter disruption, and injury to levator ani muscles.4-8 Pelvic floor anatomical evaluation over time can assist in tracking how pelvic structures recover after vaginal delivery, particularly after births with higher tissue trauma potential. These issues are relevant because of the links between vaginal birth, damage to the levator ani muscles and pelvic organ prolapse. For instance, one study showed that fifty-five percent of women with prolapse have major levator injuries compared with 16% of women with normal support; an odds ratio of 7.3.9

Studies have evaluated pelvic floor locations and dimensions of different pelvic floor structures in parous women using MR imaging in the postpartum period to evaluate static resting position,10,11 using MR imaging during straining to compare parous to nulliparous women,12 or using ultrasounds before and after deliveries.13 However, these studies are limited by their cross-sectional design, short postpartum follow-up time, and/or not evaluating dynamic properties with both Kegel and Valsalva maneuvers. Moreover, these prior studies targeted women at normal risk for pelvic floor injury and include relatively few women at highest risk for soft tissue trauma who can be expected to have injuries. This latter group is of most special interest when investigating pelvic floor disorders. To address these gaps in the literature, we designed a study to evaluate: 1) comparative location of pelvic structures at rest (“sagging”) early and late postpartum, and 2) the movement that occurred during Kegel or Valsalva in a cohort of women known to have had obstetric events associated with soft tissue injury. We employed dynamic MR imaging and image analysis.

Materials and Methods

Study Design and Sample

The parent study, Evaluating Maternal Recovery from Labor & Delivery 1 (EMRLD 1), was a pilot study examining the use of magnetic resonance imaging in tracking levator ani injury recovery in primiparous women in the early and late postpartum time. We recruited 19 primiparous women who had recently delivered (within the past two weeks) and had obstetric factors deemed a priori to be associated with levator ani injury.14 These factors included forceps or vacuum delivery, anal sphincter laceration, prolonged second stage of labor, precipitous delivery, and shoulder dystocia.

All procedures were approved by the Institutional Review Board (IRB#2005-0011). Potentially qualifying participants were identified by a chart review. Information about the study was provided at a hospital visit immediately postpartum or by a follow-up letter if logistics prohibited personal contact. Individual screening for full inclusion/exclusion criteria was done by study personnel over the phone. Women were screened out if they did not speak English, were claustrophobic or had other factors that limited ability to have serial MRI’s, or factors that otherwise jeopardized likelihood of retention in this pilot longitudinal study, for instance transportation difficulties. We did not systematically screen women either in or out of the study on the basis of pelvic floor disorders.

Postpartum MR scans were taken early (mean ± SD: 29.4 ± 8.7 days or approximately 1 month) and late after delivery (mean 207.9 ±14.3 days or approximately 7 months), hereafter referred to as “early” and “late” time-points. At each MR visit, instructional coaching for performing Kegel and Valsalva maneuvers was consistently done by a single experienced technologist. MR imaging for this study was conducted on a 3 Tesla, Philips Achieva machine (Philips Medical Systems, The Netherlands) using an 8 channel cardiac coil positioned over the pelvis) included single shot TSE sequences FOV 340, 6mm slice 0 gap, TE 105, TR 1400, NSA 1, 90 flip angle, matrix 256×90, dynamic 20 scans in rest, Kegel and Valsalva maneuvers.

Specific MR images were then chosen for evaluation by the following criteria: at pre-Kegel (Kegel-rest, the first image before starting Kegel), at maximum Kegel (the image with the highest bladder neck elevation), at pre-Valsalva (Valsalva-rest, the first image before starting Valsalva), and at maximum Valsalva (the image with the lowest bladder neck descent) (Figure 1).

Figure 1
MR images at Rest, Kegel and Valsalva. Three panels figure showing mid-sagittal MR images at Rest, maximum Kegel and maximum Valsalva at early (~1 month) postpartum.

The images were then converted from DICOM into JPEG format. The JPEG images were arranged in a PowerPoint presentation where diagrams would be drawn, images could be rotated to make axes consistent, and that point placement verification could be carried out prior to measurement. Each diagram contained: the sacro-coccygeal inferior pubic point (SCIPP) line, the levator hiatus, the levator plate angle, the perineal body, the anal verge, the bladder neck, and the cervix (Figure 2). During the drawing of these locations and diameters, care was taken to make sure that the drawn dot represented the same location within the tissues by rapidly alternating between rest, Kegel and Valsalva slides. A second rater [JD] confirmed the drawn locations and diameters prior to measurement. A measurement technique similar to that described by Boyadzhyan et al. and Hsu et al. was used.15,16

Figure 2
Measurement scheme. 2a) Mid-sagittal MR image at rest with the locations, diameters and angle measured. 2b) Schematic representation of SCIPP line and the axes.

Figure 2 shows mid-sagittal MR image at rest (2a) and schematic representation (2b). For measurement purposes, the SCIPP line was considered as the x-axis, and a line was drawn perpendicular to it (y-axis). (-) y values are shown superiorly so that larger degrees of descent are associated with more positive numbers, as has been custom in pelvic floor measurements. Measures were obtained to mark locations of the levator hiatus, urogenital hiatus, levator plate angle, perineal body (PB), anal verge, bladder neck (BN) and cervix (Figure 2a).

Using Image J1.41 (NIH) software,17 the locations of the perineal body, anal verge, bladder neck and cervix were determined as x and y coordinates, with the origin set at the inferior pubic point and the x-axis aligned with the SCIPP (Figure 2b). The urogenital hiatus was measured from the inferior aspect of the pubic bone to the perineal body just in front of the anal sphincter, and the levator hiatus from the same pubic point to the inner surface of the levator at its narrowest diameter. The angle of the levator plate was measured relative to the SCIPP line. When the levator plate was parallel to SCIPP line, the angle was considered zero; when it was above to parallel in a clockwise direction, the angle was considered negative; and when it was below to parallel in a counter-clockwise direction, the angle was considered positive. Using the x and y coordinates of the various structures, displacements from rest to maximum Kegel as well as from rest to maximum Valsalva were calculated. The resting locations, diameters and angles were taken as the average measures of pre-Kegel (Kegel-rest) and pre-Valsalva (Valsalva-rest).

Statistical Analysis

This is a secondary analysis from a parent study hence, prospective power analysis was not performed and we evaluated images from all 19 women. Due to the small sample size and lack of normal distribution, the nonparametric Wilcoxon Signed Rank Test was used for determining differences in measures made at early and late time points. Significance was placed at p values less than 0.05. We calculated effect size (r) as = z /√(2×n). SPSS version 16.0 software was used. Data were reported as medians and the inter-quartile range was accompanied (the range between the 25th and the 75th percentiles).

Results

The sample showed a mean(sd) age of 28.6(3.6) years, BMI of 25.6(4.0), and racial distribution of 83.3% Caucasian, 11% Asian, and 5.6% other race. At the late visit, in response to the question, “In the last month, have you involuntarily lost or leaked any amount of urine or been unable to hold your water and wet yourself?” 61.5% of the sample responded “yes”. None of the women had pelvic organ prolapse below the level of the hymen on clinical examination. Thirteen image pairs MR images were suitable for analysis. Images were excluded for three women who did not have late scan and 3 women whose images revealed motion artifact of parasagittal rather than sagittal image location. Comparisons were made between rest locations (x and y coordinates) of the perineal body, anal verge, bladder neck and cervix in these women at early versus late postpartum (Figure 3, Table 1). At rest, a statistically significant increase in both the perineal body and the anal verge vertical locations (y-coordinate) on late scans were seen (7.1 mm and 7.9 mm, respectively, p = 0.003). The effect sizes for the y-coordinates were large (r > 0.5) for both the perineal body and the anal verge. The x coordinates were not significantly different. There were no significant differences in the rest locations of the bladder neck or the cervix, although at this small sample size, results are not conclusive. The effect size for change in the y-coordinate of the bladder neck was r = -0.34.

Figure 3
Pelvic floor structures locations. Approximate locations of the Perineal Body (PB), Anal verge, Bladder Neck (BN), and Cervix at rest, maximum Kegel and maximum Valsalva at early (~1 month) and late (~7 months) postpartum shown in the upright posture ...
Table 1
Structures Locations at Rest

Displacement during Kegel and Valsalva maneuvers were similar when late measures were compared to early postpartum measures for all of the measured pelvic structures observed on dynamic MR images (Figure 3, Table 2).

Table 2
Displacements Magnitude during Kegel and Valsalva

At rest, changes in the urogenital and the levator hiatus diameters between early and late postpartum were also assessed. The rest diameters were smaller on the late scans compared with the early scans by 7.7 mm and 3.2 mm respectively (p < 0.05) (Figure 4, Table 3). This was true at maximum Kegel and maximum Valsalva as well.

Figure 4
The urogenital hiatus and levator hiatus diameters. The urogenital hiatus and levator hiatus diameters at rest, maximum Kegel and maximum Valsalva at early (~1 month) and late (~7 months) postpartum shown in the upright posture, diagrammatically showing ...
Table 3
Levator and Urogenital hiatus diameters

No differences were seen between the levator plate angle at early versus late postpartum at rest, Kegel or Valsalva (Table 4). The maximum Kegel angles were always negative (counter-clockwise) while the maximum Valsalva angles were always positive (clockwise), confirming that women were correctly responding to the verbal instructions on Kegel, or Valsalva.

Table 4
Levator Plate Angle (relative to SCIPP line) (degree)

In this small sample size, there did not appear to be an obvious pattern in the different measurements by levator ani muscle status judged as intact versus any tear (defect).18 To demonstrate this point, we provide the graphical presentation of individual data by levator status in Figure 5A (perineal body rest locations) and Figure 5B (anal verge locations).

Figure 5
5a) The individual locations of the perineal body (PB) at early and late postpartum with color codes indicating an individual with a levator ani defect (tear). 5b) The individual locations of the anal verge at early and late postpartum with color codes ...

Comment

The rest locations of the perineal landmarks, namely the perineal body and the anal verge, are higher at late (~7 months) compared to early (~1 month) postpartum in a group of women who all had birth risk factors associated with levator ani injury. Unexpectedly, the amount of pelvic floor movement during Kegel and Valsalva did not differ between early and late postpartum scans.

Our findings concerning the pelvic floor locations at rest are similar to those previously reported in indicating progressive elevation over time. In addition, our findings extend the current literature by adding information about location and movement during Valsalva and Kegel maneuvers. Hayat et al. studied the urethrovesical angle, urethral length, distance from the symphysis to the proximal and distal vagina, vaginal length, and width and length of the sphincters in MR images of pregnant women at several time points between 1 week to 6 weeks postpartum.10 They found that the distance between symphysis and distal vagina changed significantly over time but without a clear trend in direction (p = 0.01). However, this study differed from ours in that it did not study the same parameters and also only used static images at rest. Tunn et al. studied perineal body and levator and urogenital hiatus sizes in the same set of women and also using static MR imaging at rest.11 This study concurs with our findings that rest locations improve over time. They showed that the perineal body distance from SCIPP line shortens by 13.4 ±7.3 mm (p < 0.05) at 2 weeks compared to 1 day postpartum in a group of six women using static MR images. However, this difference at rest is larger than the difference we found between early (~1 month) and late (~7 months) postpartum. This lends credence to the expectation that the bulk of recovery takes place in the early postpartum period.

The fact that location changes, but movement does not, suggests that perineal position and muscle function demonstrated as excursion during a pelvic muscle contraction are different phenomena. Several types of muscle impairment can occur with birth: 1) static factors (the resting muscle tone and connective tissue reflected by measuring the rest locations) and 2) the ability to volitionally contract and relax the muscles (reflected by measuring displacements during Kegel and Valsalva). Our findings can be explained when considering the contribution of both the muscles’ and the connective tissues’ involvement, since pelvic viscera are held by the connective tissues as well as by the resting tone of smooth and striated muscles. Measurements made in the supine position, as is typically done during pelvic examination, present minimal resistance on the muscles because they are unloaded; thus supine displacement during muscle contraction is not an indicator of maximum muscle strength since load carrying is minimized. It would be ideal to obtain images in the standing position, but at present, limitations in open magnet configuration, magnet strength and blurring from subject motion while standing make this approach unfeasible. Functionally though, all women were able to elicit an upward movement when asked to contract as evidence by the levator plate angle measurements.

Further confirmation that the rest locations may be more dependent on static factors comes from evaluating the urogenital hiatus and the levator hiatus diameters at rest. The urogenital hiatus and the levator hiatus turned out to be significantly smaller late postpartum. A similar study evaluated the postpartum changes at rest only in 6 women found that at 2 weeks postpartum there is decreased area (which involves both width and length) of the urogenital hiatus by 27% (p < 0.05) and of the levator hiatus by 22% (p < 0.05) compared to 1 day postpartum.11 It is not possible to separate connective tissue and muscles at rest. Whether the changes in resting position reflect connective tissue healing or changes in the set point of resting muscle activity will require further investigation.

Several factors in our study must be kept in mind in interpreting our results. Our findings concern changes after delivery and do not allow us to say whether this is a return to the normal pre-birth situation. In addition, the small sample size limits our ability to look for interactions between variables and subtle changes may not be detectable. Because the uterus is visible in the images and it changes in size significantly from one to seven months postpartum, it was not possible to be completely blinded to the time point. In addition, it was necessary to compare point placement before and during the maneuvers, which also precluded complete blinding. Other factors that might have affected our study are that participant performance of Kegel/Valsalva was inconsistent over time, or that coaching instructions differed by time point. The latter is particularly unlikely, however, considering the single technologist taking all measures and her sound prior experience and consistency.

Our study has evaluated the rest locations and the movements of pelvic structures in the same individual following high risk vaginal delivery at early (~1 month) versus late (~7 months) postpartum using dynamic MR imaging taken at rest, during Kegel and during Valsalva. It extends the current literature by looking at muscle contraction and Valsalva in conjunction with resting anatomical locations. We followed women longitudinally from early to late postpartum, long enough to reflect women’s return to normal activities. It is also a study that specifically targets women known to have obstetrical risk factors associated with soft tissue injury, such as levator ani tear.

  • Levator ani morphological and functional evaluation after vaginal delivery can help determine post-birth recovery processes, which is important because of the direct link between it and levator ani muscles damage and pelvic organ prolapse.
  • Studying the functional recovery enhances our understanding of the types of muscle impairments that can occur and have lasting implications after vaginal birth.
  • Dynamic MRI is a strong tool in evaluating the functional muscle impairment after vaginal delivery as examined during muscle work of Kegel and Valsalva.
  • As there is no existing method of evaluating the recovery of pelvic floor after vaginal delivery, we tried to understand the patho-anatomy of this process and target the parameters that might be most helpful to gain an understanding of recovery.

Acknowledgments

We gratefully acknowledge study support from the NICHD Grant R21 HD 049818 for this research and additional investigator support from Office for Research on Women’s Health SCOR on Sex and Gender Factors affecting Women’s Health P50 HD 44406

Footnotes

Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

The research was presented in 35th annual meeting of the Society of Gynecologic Surgeons’ scientific meeting in New Orleans, LA (March 30-April 1, 2009)

Condensation:

The perineal structures are higher at rest at seven months compared to one month postpartum, but movement during Kegel and Valsalva do not change.

References

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