Defining “normal recovery” of pelvic floor function and appearance in a high-risk vaginal delivery cohort

Abstract

Introduction and Hypothesis:

Childbirth pelvic floor trauma leads to pelvic floor disorders. Identification of significant injuries would facilitate intervention for recovery. Our objectives were to identify differences in pelvic floor appearance and function following delivery and identify patterns of normal recovery in women sustaining high-risk labor events.

Methods:

We completed a prospective cohort study comparing women having vaginal births with risk factors for pelvic floor injury to women having cesareans. Data were collected on multidimensional factors including levator ani muscle (LA) tears. Descriptive and bivariate statistics were used to compare the groups. We identified potential markers of pelvic floor injury based on effect size.

Results:

Eighty-two women post vaginal delivery and 30 women post cesarean enrolled. The vaginal group had decreased perineal body length between early postpartum, six weeks (p<0.001), and six months (p=0.001). POP-Q points did not change between any time point (all p>0.05). Measures of strength improved between each time point (all p<0.002). When compared to cesarean, women post vaginal birth had longer genital hiatus and lower anterior and posterior vaginal walls (all p<0.05).

Based on theoretical considerations and effect sizes, those with Bp ≥0 cm, Kegel force ≤1.50 N, and/or an LA tear on imaging were considered to have significant pelvic floor injury. Using this definition, at six weeks, 27 (46.4%) women were classified as injured. At six months, 13 (29.6%) remained injured.

Conclusions:

We propose pelvic floor muscle strength, posterior vaginal wall support, and imaging consistent with LA tear as potential indicators of abnormal or prolonged recovery in this cohort with high-risk labor events.

Brief Summary:

Diminished strength, posterior vaginal wall descent, and levator injury are potential markers of non-recovery from childbirth in women at high risk for pelvic floor damage.

Introduction:

Pelvic floor disorders (PFD) affect as many as 28 million women in the United States, with the peak incidence occurring in the sixth decade of life [1,2]. Vaginal childbirth is one of the strongest risk factors for pelvic floor disorders, presumably due to injuries to connective tissues and/or muscular support of the pelvic organs sustained at the time of childbirth [3]. Studies aiming to prevent pelvic floor disorders with postpartum inventions such as physical therapy have not demonstrated consistent benefit to asymptomatic women [4,5]. This is likely due to the fact that while PFDs are frequently related to injury sustained at childbirth, they most often present later in life [3]. Understanding how women recover from childbirth is key to early identification of potentially clinically significant but asymptomatic injuries. Women who display signs of differential recovery represent a potential population for early intervention and investigations into secondary prevention/mitigation of future pelvic floor disorders.

Investigators have reported results in several recent studies focused on pelvic floor changes that occur in healthy women after the first vaginal birth. They have not, however, identified clinically significant differences in function or symptoms [6-9]. In these studies, they identified that the vast majority of women recovered function and appearance similar to their pre-childbirth state and similar to women who had cesarean deliveries by six months postpartum [6-8]. However, longitudinal work by Blomquist et. al. has confirmed the association between vaginal childbirth and a range of pelvic floor disorders [10]. This is arguably because many injuries are subclinical in the first year after birth, and healthy women have very low rates of injury. Attempting to identify a specific population for preventative intervention studies in the general (low-risk) postpartum population does not adhere to best practices for prophylaxis or intervention, as the prevalence does not warrant utilization of these resources.

Therefore, we undertook a prospective cohort study of women with known high risk factors for tearing the levator ani (LA) muscles based on previous studies. Injury from vaginal childbirth can be evident in the absence of an identifiable LA tear and some risk factors for levator tearing also impart risk for PFDs in the absence of visable damage to the muscle [10-13]. Our objective was to identify differences in pelvic floor appearance and function immediately postpartum, two to six weeks after birth, and six months postpartum and to document the process of normal recovery in this cohort of women sustaining high-risk labor events (referred to as “high-risk” for remainder of manuscript). For a control group, we compared these women at high risk for injury to women experiencing pregnancy but not second stage labor and vaginal delivery.

Understanding recovery in this population with higher risk for injury—and higher pretest probability of injury—is vital to identifying a select population that could potentially benefit from preventative interventions.

Materials and Methods

After obtaining Institutional Review Board approval, women were recruited within 48 hours after delivery at the University of Michigan birth center between August 2014 and July 2016. This was a convenience sample of women who were postpartum on the labor and delivery unit on days when the research team was available for recruitment. All participants provided written informed consent.

All participants recruited were age ≥18 years, were able to read English, had an absence of serious medical problems for the infant and mother, and had delivered at gestational age ≥32 weeks. Participants were recruited for two cohorts: 1) women who experienced their first vaginal birth, and 2) women who had their first or second cesarean delivery, with no history of second stage of labor. Inclusion criteria for the vaginal delivery group were having one or more of the following risk factors with first vaginal birth: forceps delivery [14,15], vacuum delivery [16], active pushing >150 minutes [14,17], episiotomy [14,18], and/or anal sphincter laceration [14]. The cesarean delivery cohort included women having their first or second cesarean delivery without prior history of entering the second stage of labor. Second-time mothers were included for ease of recruitment, as the majority of planned cesareans were repeat surgeries and did not differ meaningfully from first-time mothers on the basis of age, BMI, or anatomical and functional assessments (data not shown).

Anatomical and Functional Assessments

All participants had standardized physical exams and functional assessments within 48 hours of delivery on the hospital unit (i.e., early postpartum exam). Early postpartum exams were designed to assess the pelvic floor with minimal discomfort to the participant. Exams were performed by authors PSF, DEF, and LKL utilizing a checklist of the exam components. Prior to formal data collection, examiners performed exams together for a trial period to ensure that similar techniques were used. This early postpartum exam included testing of bulbocavernosus and anal wink sacral spinal reflexes, assessment of pelvic floor muscle strength using the Modified Oxford score [19,20], and measurement of pelvic organ prolapse quantification system (POP-Q) [21] points GH and PB at strain and at rest.

Women in the high-risk vaginal birth group had comprehensive physical exams and functional assessments once or twice (as clinically indicated) between two and six weeks, then again at six months postpartum. Those in the cesarean delivery group had physical exams and functional assessments at six weeks and six months postpartum. Authors PSF and DEF performed all clinical exams in the clinic setting. Exams were standardized between the examiners through use of joint examinations and observation. Data collected at the clinical visits included testing of sensation in sacral nerve root distribution, bulbocavernosus and anal wink reflex, full POP-Q [21] exam, assessment of pelvic floor strength by palpation using the Modified Oxford score [19,20], and objective assessment of strength using the instrumented speculum described previously by Ashton-Miller [22]. The instrumented speculum is a validated and reliable device that measures force generated by pelvic floor muscle contraction in Newtons (N) [22].

Imaging

At each examination point, participants underwent transperineal 2D ultrasound to assess objective movement of the bladder base with pelvic floor muscle contraction. The 2D curvilinear 8820e transducer (6-2 MHz) was placed on the vulva to obtain sagittal imaging of the pubic bone, urethra, and bladder neck. Participants were asked to perform a Kegel, with the examiner recording whether movement of the base of the bladder with muscle contraction was present or absent. If the participant pushed or was unable to contract, examiners coached the patient briefly and testing was repeated.

At the 6-week and 6-month exams, 3D transvaginal imaging was performed to evaluate for LA tears. These ultrasounds were independently reviewed by authors JOD, PSF, and DEF. Reviewers were blinded to delivery status of the participants. The LA were evaluated in multiple planes to determine injury status. Sides were graded as no tear, partial tear, or full thickness tear. Based on ultrasound review, three groups were created: 1) no tear; 2) minor tear(unilateral partial tear); and 3) major tear (bilateral partial or any full thickness tear). Reviews were performed independently and adjudicated by group consensus in the case of discrepant results.

Statistical Analysis

Study data were collected and managed using REDCap electronic data capture tools hosted at the Michigan Institute for Clinical & Health Research at the University of Michigan. All analyses were conducted in Stata v. 14.1 (StataCorp. 2013. Stata Statistical Software: Release 14. College Station, TX: StataCorp LP.)

Descriptive statistics, including means and proportions, are presented separately for the high-risk vaginal birth and cesarean groups for demographic statistics, early postpartum exam measures, and the LA tear rate. Clustered bar charts were used to visually represent measures of function and appearance over time and between groups. Simple linear regressions were used to assess group differences for continuous measures of interest, and simple binary logistic regressions were used for binary measures. Measures of effect size include Cohen’s d for continuous measures and odds ratios for binary measures. Within both the high-risk vaginal birth and cesarean groups, differences in function and appearance between the study period time points were assessed with paired t-tests for continuous measures and McNemar’s test for binary measures. Using the effect size of differences between groups and theoretical considerations we developed an operational definition for significant pelvic floor injury sustained from delivery. Simple logistic regressions were used to associate baseline measures, anatomic assessments, and pelvic floor function measures with our operational definition of pelvic floor injury at six months postpartum.

Results

At the conclusion of the enrollment period, 112 women consented to participate in the study: 82 (72.3%) with high-risk vaginal births and 30 (26.8%) cesarean controls (Figure 1). Of the 112 women who participated in the early postpartum data collection, 79 (70.5%) had an exam 2-6 weeks postpartum, and 61 (54.5%) had 6-month exams. Complete data for each time point was available for 37 (45.1%) high-risk vaginal births and 16 (53.3%) cesarean controls.

Figure 1. Enrollment and Loss to Follow-up.

Flow chart of enrollment and loss to follow-up at each time point.

^aNot all women able to tolerate exam due to discomfort

^bInconvenience of visits, moved out of town, unable to contact

Demographics of the two study populations are shown in Table 1. Both groups were primarily white, with normal mean BMI and mean age in the early 30s. Compared to women who had high-risk vaginal births, women in the cesarean group were three years older (33 v 30 years, p=0.02). In the high-risk group, 15.9% had instrumented delivery, 47.5% had anal sphincter laceration, 9.8% had episiotomy, and 57.6% had prolonged active pushing in the second stage. In the vaginal birth group at six weeks, 24 (42.8%) women had an LA tears identified on ultrasound. One woman declined ultrasound due to discomfort. Fourteen women had major tears (25%) and 10 (17.8%) had minor tears. At six months, seven women had major tears (15.9%) and three had minor tears (6.8%). There were no LA tears identified in the cesarean control group at either time point.

Table 1.

Group Demographics and Delivery Data^a

	High-Risk Vaginal Births n=82	Cesarean Births n=30	p-value
Age (years)	29.9 (28.8-31.1)	32.6 (30.9-34.39)	0.02
BMI (kg/m2)	31.2 (30-32.4)	32.5 (30.4-34.5)	0.3
Race (%)			0.4
White	78 (67.5-86.4)	80 (61.4-92.3)
African American	6.1 (2-13.7)	13.3 (3.8-30.7)
Asian	8.5 (3.5-16.8)	0.0 (0-11.6)
Hispanic	2.4 (0.3-8.5)	3.3 (0.08-17.2)
Arabic/Middle Eastern	2.4 (0.3-8.5)	0.0 (0-11.6)
Other	2.4 (0.3-8.5)	3.3 (0.08-17.2)
Gestational Age (weeks)	40.1 (39.6-40.6)	39.6 (38.5-40.8)	0.4
Fetal Birthweight (g)	3478.4 (3373.8-3583.1)	3458.6 (3227.1-3690.2)	0.9
Induction of Labor (%)	26.8(17.6-37.8)	20.7 (8-39.7)	0.6
Length of Second Stage (min)	157.8 (128.2-187.3)	-	N/A
Vacuum-Assisted (%)	12.2 (6-21.3)	-	N/A
Forceps-Assisted (%)	3.7 (0.8-10.3)	-	N/A
Perineal Trauma (%)			N/A
1st Degree Laceration	10 (4.1-19.5)	-
2nd Degree Laceration	34.3 (23.4-46.6)	-
3rd Degree Laceration	47.1 (35.1-59.5)	-
4th Degree Laceration	8.6 (3.2-17.7)	-
Episiotomy (%)	9.8 (4.3-18.3)	-	N/A

^aData expressed as value (95% CI)

Figure 2 shows anatomic assessments for each group at each time point. The most dependent parts of the anterior and posterior vaginal walls (POP-Q points Ba and Bp, respectively) were closer to the hymen in the vaginal birth group as compared to the cesarean group. When compared to those undergoing cesarean delivery, women in the vaginal birth cohort had longer mean genital hiatus (GH) at all time points (all p<0.002); however, perineal body size only differed at the early postpartum exam, with the vaginal birth group being longer (p=0.002). Over time, women in the cesarean delivery group had no meaningful changes for point Ba, point Bp, or GH (all p>0.05). However, perineal body length decreased slightly between the early postpartum and 6-month measures (p=0.04). For the vaginal delivery group, perineal body length decreased between early postpartum and six weeks (p<0.001) and at six months (p=0.001), but there was no difference between six weeks and six months. Points Ba, Bp, and GH did not change substantively between any of the time points for either vaginal or cesarean deliveries (all p>0.05).

Figure 2. Measures of Vaginal Support and Perineal Anatomy.

Mean POP-Q measurements at each time point measured for high-risk vaginal births and cesarean deliveries. P-values represent comparisons between vaginal and cesarean deliveries.

Error bars demonstrate standard deviations.

POP-Q: pelvic organ prolapse quantification

^aNo cesarean deliveries had exam at 2-week time point

Measures of pelvic floor function are shown in Figure 3. Women in the cesarean delivery group had stronger pelvic floor strength as measured by Oxford score at 48 hours postpartum (p<0.001), and as measured by Oxford score and instrumented speculum at six weeks (p=0.002) compared to women in the high-risk vaginal group. At the early postpartum exam, women in the cesarean delivery group more frequently demonstrated bladder lift on ultrasound and had bilateral anal wink reflex present compared to the vaginal delivery group. For within-group change, women in the cesarean delivery cohort demonstrated an increased Oxford score between early postpartum and six weeks (p=0.01), but not at any other time point (all p>0.05). In the high-risk vaginal delivery group, the proportion of women who demonstrated lift on ultrasound increased between each time point, as did the proportion with intact anal wink (with statistically significant change between early postpartum and six months [p=0.04]), but not meaningfully between any other time points (all p>0.05). Strength, as measured by Oxford score and Kegel force by instrumented speculum, improved between each time point (all p<0.002) for both vaginal and cesarean births.

Figure 3. Measures of Pelvic Floor Function.

Mean measures of pelvic floor muscle strength and proportions of births with anal wink sacral reflex and ultrasound observation of bladder movement at each time point measured. P-values represent comparisons between vaginal and cesarean deliveries. Error bars demonstrate upper and lower bounds of 95% confidence intervals for proportions and standard deviations for means.

^aNo cesarean deliveries had exam at 2-week time point

Table 2 describes the magnitude of the difference between the groups at each time point for anatomic assessments and measures of pelvic floor function. A number of measures indicated a moderate or strong difference between women in the high-risk vaginal birth group compared to women in the cesarean delivery group at six weeks and six months postpartum, including Kegel force and points Bp, Ba, and GH. To create an operational definition for injury at six weeks and six months for women in the high-risk vaginal birth group, we first looked to these measures with notable differences between the groups in conjunction with theoretical considerations. Women in the high-risk vaginal birth group who had extreme values for these measures would likely be considered injured clinically, so women in the worst 10% of the distribution were flagged as potentially injured. Alternative cutoffs for extreme values were considered, such as the worst 25% for a measure, but subsequent sensitivity analyses deemed the alternatives as non-informative.

Table 2.

Differences Between High-Risk Vaginal Births and Cesarean Controls^a

	High-Risk Vaginal Births	Cesarean Births	Effect Size	p-value
48-hour Postpartum Exam	N=79	N=29
Genital Hiatus (cm)	3.7 (3.5-3.9)	2.1 (1.9-2.3)	2.1	<0.001
Oxford Score (summed bilateral)	1.9 (1.4-2.4)	5.4 (4.3-6.4)	1.5	<0.001
Perineal Body (cm)	4.8 (4.5-5.1)	4 (3.6-4.3)	0.7	0.002
POP-Q C (cm)	−6.5 (−7.1-5.9)	−7.8 (−8.3-7.3)	0.6	0.01
Bladder Elevation on US (%)	46.6 (34.8-58.6)	76 (54.8-90.6)	0.3	0.01
Presence of Anal Wink (%)	60.3 (48.5-71.2)	89.7 (72.7-97.8)	0.2	0.008
6-Week Postpartum Exam	N=56	N=23
Genital Hiatus (cm)	3.2 (3-3.4)	2.4 (2.1-2.6)	1.2	<0.001
POP-Q Ba (cm)	−1.5 (−1.8- −1.2)	−2.6 (−2.9- −2.4)	1.1	<0.001
POP-Q Bp (cm)	−2 (−2.3- −1.7)	−2.8 (−3- −2.6)	0.9	0.001
Oxford Score (summed bilateral)	5.2 (4.4-5.9)	7.4 (6.2-8.5)	0.8	0.002
POP-Q C (cm)	−7.5 (−7.9- −7.1)	−8.5 (−9.1- −7.6)	0.7	0.005
Maximum Kegel Force (N)	3.3 (2.8-3.7)	4.5 (3.7-5.4)	0.7	0.006
Presence of Anal Wink (%)	67.9 (54-79.7)	73.9 (51.6-89.8)	0.7	0.6
Vaginal Resting Force (N)	1.7 (1.5-2)	2.19 (1.6-2.8)	0.5	0.07
Bladder Elevation on US (%)	72.3 (57.4-84.4)	95.2 (76.1-99.9)	0.1	0.06
Perineal body (cm)	3.6 (3.4-3.9)	3.7 (3.3-4.2)	0.1	0.6
6-Month Postpartum Exam	N=44	N=17
Genital Hiatus (cm)	3 (2.8-3.2)	2.2 (1.8-2.6)	1.1	<0.001
POP-Q Bp (cm)	−2 (−2.4- −1.7)	−2.8 (−3- −2.6)	0.9	0.004
POP-Q C (cm)	−7.2 (−7.7- −6.72)	−8.4 (−9.06- −7.64)	0.8	0.008
POP-Q Ba (cm)	−1.7 (−2- −1.5)	−2.4 (−2.8- −2)	0.8	0.009
Presence of Anal Wink (%)	81.8 (67.3-91.8)	88.2 (63.6-98.5)	0.6	0.5
Bladder Elevation on US (%)	87.8 (73.8-95.9)	93.8 (69.8-99.8)	0.5	0.5
Maximum Kegel Force (N)	4.2 (3.5-4.9)	5.1 (3.9-6.3)	0.4	0.2
Oxford Score (summed bilateral)	6.2 (5.4-7.1)	7.3 (6.2-8.5)	0.4	0.2
Vaginal Resting Force (N)	1.9 (1.7-2.1)	2.1 (1.7-2.5)	0.3	0.3
Perineal body (cm)	3.6 (3.3-3.9)	3.5 (3.1-3.9)	0.08	0.8

^aData expressed as mean (95% CI) or percent (95% CI)

POP-Q=pelvic organ prolapse quantification

Measures that represent different dimensions of injury were considered in combination with each other. Maximum Kegel force measures both pelvic floor function and anatomy, as a woman must voluntarily contract intact pelvic floor muscles and damage to the neuromuscular anatomy may prevent this function. Posterior vaginal wall position (BP) as measured on the POP-Q system is an anatomical variable that may be altered with connective tissue or muscle damage. The status of the LA muscles is a direct anatomical measurement, which is included due to the established association between LA tears and PFD risk. Subsequently, those in the high-risk vaginal birth group with either the worst 10% for POP-Q Bp (≥0 cm), or the worst 10% for Kegel force (≤1.50 N), or an LA tear were considered injured. Injury classifications were made at six weeks and six months postpartum.

At six weeks, 28 (49.1%) women in the high-risk vaginal birth group were classified as injured based on our operational definition described above. By six months, 13 (29.6%) were considered injured. When comparing 6-week and 6-month injury classifications, for those with measurements at both six weeks and six months, eight (40%) of those injured at six weeks recovered by six months. Twelve (60%) women injured at six weeks did not demonstrate recovery at six months. All 18 women without injury at six weeks were without injury at six months.

Demographics, anatomic assessments, and measures of pelvic floor function at 48 hours and six weeks for high-risk vaginal births with and without injury are presented in Table 3. Size of the GH within 48 hours of delivery is predictive of injury at six months (OR=3.3, 95% CI=1.06-10.2, p=0.04). The 6-week Oxford score is marginally predictive (OR=0.78, 95% CI=0.60-1.02, p=0.07), with lower Oxford scores being associated with injury. A breakdown of individual characteristics that qualified participants as “injured” by our operational definition is provided in Table 4.

Table 3.

Associations with Being Injured and Uninjured 6 Months after High-Risk Vaginal Birth^a

	Injured N=13	Uninjured N=31	Odds Ratio Predicting Injury (95% CI)	p-value
Demographics
Age (years)	31.8 (28.4-35.2)	30.4 (28.5-32.4)	1.1 (0.9-1.2)	0.5
Gestational Age (weeks)	39.8 (39.1-40.5)	40 (39.1-40.69)	1 (0.7-1.3)	0.8
Fetal Birthweight (g)	3589.7 (3284.6-3894.8)	3405.8 (3214-3597.6)	1 (0.999-1.002)	0.3
BMI (kg/m2)	30.4 (27.4-33.4)	31.9 (29.8-33.9)	0.9 (0.8-1.07)	0.4
Infant Head Circumference (cm)	34.9 (34.2-35.6)	34.3 (33.8-34.8)	1.4 (0.9-2.3)	0.2
48-hour Postpartum Exam
Genital Hiatus (cm)	4.1 (3.4-4.9)	3.5 (3.3-3.7)	3.3 (1.1-10.2)	0.04
Oxford Score (summed bilateral)	2.6 (0.8-3.5)	2 (1.2(2.8)	1.04 (0.8-1.4)	0.8
Perineal Body (cm)	4.9 (4-5.8)	4.4 (4-4.9)	1.3 (0.8-2.3)	0.3
POP-Q C (cm)	−6.1 (−8.3- −3.8)	−6.6 (−7.5- −5.7)	1.1 (0.8-1.4)	0.6
Bladder Elevation on US (%)	41.7 (15.2-72.3)	42.9 (24.5-62.8)	1 (0.2-3.7)	0.9
Presence of Anal Wink (%)	76.9 (46.2-95)	50 (31.3-68.7)	3.3 (0.8-14.6)	0.4
6-Week Postpartum Exam
Genital Hiatus (cm)	3.4 (2.9-3.8)	3.1 (2.8-3.4)	1.7 (0.6-4.7)	0.3
POP-Q Ba (cm)	−1.9 (−2.1- −0.6)	−1.6 (−2.1- −1.1)	1.2 (0.6-2.2)	0.6
POP-Q Bp (cm)	−1.1 (−1.9- −0.3)	−2.4 (−2.7- −2)	3.2 (1.4-7.4)	0.005
Oxford Score (summed bilateral)	3.7 (2.1-5.3)	5.8 (4.6-7.1)	0.8 (0.6-1.01)	0.07
POP-Q C (cm)	−7.2 (−8.4- −6.2)	−7.6 (−8- −7.1)	1.3 (0.7-2.2)	0.4
Maximum Kegel Force (N)	2.7 (.6-3.8)	3.5 (2.8-4.1)	0.7 (0.4-1.2)	0.2
Presence of Anal Wink (%)	72.7 (39-94)	69.2 (48.2-85.7)	1.2 (0.2-5.7)	0.8
Vaginal Resting Force (N)	1.3 (0.8-1.9)	1.3 (1.1-1.6)	0.9 (0.3-2.9)	0.9
Bladder Elevation on US (%)	55.6 (21.2-86.3)	72.7 (49.8-89.2)	0.5 (0.09-2.4)	0.4
Perineal Body (cm)	3.5 (2.6-4.3)	3.4 (3.1-3.7)	1.1 (0.5-2.3)	0.9

^aData expressed as mean (95% CI) or percent (95% CI)

POP-Q=pelvic organ prolapse quantification

Table 4.

Characteristics of Injury Classifications

Injury Status	Injury – Six Weeksa	Injury – Six Monthsb	Non- Recoverersc
Component of injury classification
POP-Q Bp (≥0 cm)	4 (7.0)	6 (13.6)	5 (42.7)
Kegel force (≤1.50 N)	4 (7.0)	4 (9.1)	3 (25.0)
Minor or major LA tear	24 (42.1)	10 (22.7)	9 (75.0)
Number of injury components for those with injury/non-recovery
1	24 (85.7)	7 (53.9)	7 (58.3)
2	3 (10.7)	5 (38.5)	4 (41.7)
3	1 (3.6)	1 (7.7)	0 (0.0)
Component mix for those with injury/non-recovery
Minor or major LA tear only	20 (71.4)	4 (30.8)	4 (33.3)
Kegel force injury only	2 (7.1)	2 (15.4)	2 (16.7)
POP-Q Bp injury only	2 (7.1)	1 (7.7)	1 (8.3)
Kegel force injury + LA tear	1 (3.6)	1 (7.7)	1 (8.3)
POP-Q Bp injury + LA tear	2 (7.1)	4 (30.8)	4 (33.3)
POP-Q Bp injury + Kegel force injury + LA tear	1 (3.6)	1 (7.7)	0 (0)

Data expressed as n (%)

POP-Q: Pelvic Organ Prolapse Quantification; LA: levator ani

^a6-week sample with individual injury component, n=28/57 (49.1%)

^b6-month sample with individual injury component, n=13/44 (29.6%)

^cRecovery/non-recovery sample with individual 6-month injury component, n=12/20 (60.0%)

Discussion

Immediately after birth, women at high risk for pelvic floor injury with their first vaginal birth had a larger GH and decreased measures of strength, as compared to women undergoing cesarean birth without pushing. The GH size became smaller over time, but did not return to Similarly average lengths of women in the cesarean delivery group. Measures of strength also improved over time for women with high-risk vaginal deliveries, and by six months, strength was not statistically different between the two groups. Notably, women in the vaginal delivery group had lower anterior and posterior vaginal walls as compared to cesarean deliveries, though it should be noted that the mean POP-Q points Ba and Bp were within the normal range. Interestingly, the position of the vaginal walls did not change substantively over the three time points measured.

By defining what parameters are outside the normal range for recovery in high-risk women, we have developed a foundation for the development of early screening tools for separating normal from abnormal recovery. While tearing of the LA is a well-established risk factor for prolapse, the association between levator tears and other PFDs is less well-defined [11]. Our findings help provide insight into other potential indicators of underlying injuries that may increase future risk for PFDs. From our findings, we propose pelvic floor muscle strength, posterior vaginal wall support, and ultrasound evidence of LA tear as potential indicators of pelvic floor injury. Using this exploratory definition of injury, the size of the GH in the early postpartum period was associated with injury. In addition, pelvic floor muscle strength as measured by Oxford score was nearly statistically significant at the 6-week mark. Both of these measures are easily obtained on clinical exam and could represent a starting point for consideration of early intervention. To our knowledge, this type of screening for potential childbirth injury has yet to be described.

These analyses have limited statistical power due to the number of participants who were lost to follow-up, so further data collection at the 6-month postpartum time point is needed to fully assess our operational definition of injury. A post-hoc power analysis indicates that the Oxford score at six weeks would be predictive of injury at six months if we could compare a sample size of at least 25 injured and 25 non-injured women, assuming a 95% confidence level and the same observed effect size between those with and without injury.

Our findings regarding postpartum change in pelvic support add to the already heterogeneous literature on this topic. Regarding POP-Q points Ba and Bp, our study differs from an important prospective study of postpartum support in a healthy population that was not selected for risk factors. Reimers et al. (2016) found that POP-Q changes following delivery were transient and returned to pre-pregnancy levels by six months after delivery [9]. They also noted a difference in the change of point Ba at six weeks between women who had cesarean compared to vaginal deliveries, which resolved by six months. Consistent with our study, Rogers et al. (2014) noted a difference in points Ba and Bp at six months postpartum between low-risk women who had vaginal compared to cesarean deliveries, though the magnitude of the difference was small [7]. Regarding the length of POP-Q point GH, similar to our findings, Reimers et al. (2016) noted that it differed at all time points following delivery when comparing vaginal births to cesarean controls—a finding that was also supported by work from Elenskaia et al. (2013) [9,23]. However, in their prospective cohort study, Rogers et al. (2014) found no difference in GH size between women who experienced a first vaginal birth at low risk for negative pelvic floor changes and those who experienced cesarean deliveries [7]. Our different findings, as anticipated, reflect that women who have experienced a first vaginal birth in combination with high risk factors for negative pelvic floor changes may experience more significant changes to their pelvic support. Our results support the use of a more tailored approach to identifying those at greatest risk for negative pelvic floor changes compared to a wider approach of assuming all women would be at risk for injury post vaginal birth. The finding that pelvic floor strength is lowest after delivery and improves over time is consistent with previous studies on postpartum pelvic floor strength [6,17,23]. Our study adds to the existing body of evidence by quantifying this difference in force using an instrumented speculum that more accurately assesses muscle strength than other devices, which can be confounded by other means of generating pressure in the vagina (i.e., Valsalva) [22]. This finding was consistent for women in both the cesarean and vaginal birth groups. This may reflect women’s improved understanding of pelvic floor contraction techniques regardless of route of birth (learning bias), or, perhaps, changes to the pelvic floor that are attributable to pregnancy but not mode of delivery.

We include levator injury seen on ultrasound as an indicator because of the well-established association between injury to the levator ani and pelvic floor disorders—most significantly, prolapse [3]. Our finding of resolution levator ani damage between six weeks and six months in a subset of women is consistent with prior work by Sultan et al [24]. We felt that it was reasonable to include these women who recovered as potentially injured—and therefore potentially at higher risk of future pelvic floor disorders—because there is clearly something occurring at the level of the muscle at six weeks, even if some form of recovery or compensation occurs at a later time point. Given the small number of women sustaining LA tears (14) in this study, subanalysis relating LA tear to other parameters, or predicting co-existing factors related to LA tear, was not feasible. This is a potential direction for future investigation.

Strengths of the study include the prospective data collection by pelvic floor research experts and the recruitment design, which was intended to enrich the population with women at higher risk for pelvic floor injury. The most significant limitation is our small sample size and resulting low power to detect small differences between these two populations. It is likely that injuries sustained during childbirth have small effects initially, thus requiring a larger cohort of potentially injured women to detect the differences. The selection of cesareans as our control group is also a limitation. The use of cesarean controls was intended to maximize detection of potentially significant changes to the pelvic floor. However, low- or average-risk vaginal births would also have served as an excellent control group to confirm findings are unique to these women at higher risk of injury. We plan to confirm these exploratory findings in future studies. Further limitations include the lack of pre-pregnancy or pre-delivery data, and of full POP-Q and instrumented speculum data from the early postpartum time point. In addition, there was significant loss to follow-up at each time point, which is potentially attributable to the burden of clinical visits in the context of caring for a newborn. Similarly, performance of interrater reliability calculations was not feasible for the clinical exam components due to the burden of clinical visits on our postpartum study patients and coordination of scheduling for active clinical staff. We attempted to address this through standardization and observation; however, there may be differences in individual examiner results.

Our data show that there are detectable differences in pelvic floor appearance and function after childbirth between women having their first vaginal childbirth with known risk factors for pelvic floor disorders and women having a cesarean delivery before the second stage of labor. These differences manifested in size of the GH, strength of the pelvic floor muscles, and position of the vaginal walls. These could be used as markers to indicate the need for additional evaluation. It is necessary to further understand the mechanisms that may promote recovery from childbirth injury over time and to design interventions that may promote or normalize recovery. Women who experience specific risk factors may benefit from closer observation of their recovery course and/or specific interventions to support recovery over time.