Impact of parity on pelvic floor morphology and function: A retrospective study

Abstract

To analyze the effect of parity on pelvic floor morphology and function during the postpartum period. A total of 971 participants, who attended the Fujian Maternity and Child Health Hospital (Fuzhou, China) between December 2019 and August 2021, were included. All participants were assessed using the modified Oxford scale (MOS), pelvic floor surface electromyography, and 3-dimensional pelvic floor ultrasound to assess pelvic floor morphology and function. Multivariate analysis revealed no differences among primipara, deuteripara, and tertipara in pre-baseline rest, phasic contraction, endurance contraction, post-baseline rest, and MOS, except for tonic contraction (P = .020), the amplitude of which was lower in primipara than in deuteripara in post hoc comparison (P = .008). Differences in bladder neck presentation and bladder neck descent were statistically significant in multivariate analysis (P = .002, P = .001, respectively), with the value of bladder neck presentation in primiparas being greater than that of deuteriparas and tertipara (P = .002, P = .008, respectively), and the value of bladder neck descent was lower than that of deuteripara and tertipara in further post hoc comparisons (P = .002, P = .003, respectively). Functional impairment was not statistically associated with parity according to the MOS score or surface electromyography. However, parity was significantly correlated with descent of the bladder neck, and most of the effects appeared to occur during the first delivery.

1. Introduction

Pelvic floor dysfunction (PFD) has become an increasing concern in recent years, with its incidence being significantly higher in females than in males due to the impact of pregnancy and childbirth.^[1–5] PFDs, including pelvic organ prolapse, urinary incontinence, and sexual dysfunction, may lead to limited engagement in exercise, reduced self-image, significant economic burden, and poor quality of life.^[6–8] The occurrence and development of PFDs are closely related to changes in pelvic floor structure and function.^[9,10] Although the infant is not delivered vaginally, cesarean section (CS) and vaginal delivery (VD), which mainly occur during pregnancy, have negative effects on the pelvic floor.^[11,12] With the implementation of the Chinese 3-child policy, an increasing number of women are choosing to bear a third child, resulting in rising concerns about pelvic floor injury caused by the increased number of deliveries.^[13] Does parity affect pelvic floor morphology and function? Conflicting outcomes have been reported across different studies. Previous studies have reported that parity was not associated with the incidence of PFDs; however, others reported that parity had an impact on the development of PFDs and affected pelvic floor muscle strength (PFMS).^[14–19] As such, further studies investigating the association between parity and pelvic floor injury are warranted.

Therefore, this study aimed to evaluate the impact of parity on pelvic floor morphology and function using the modified Oxford Scale (MOS), surface electromyography (sEMG), and 3-dimensional (3D) pelvic floor ultrasonography during the postpartum period.

2. Methods

2.1. Participants

This retrospective study included 971 participants who attended the Fujian Maternity and Child Health Hospital (Fuzhou, China) between December 2019 and August 2021. This study was approved by the Ethics Committee of Fujian Maternity and Child Health Hospital (No. 2021YJ032). All patients underwent a standardized interview to assess their medical history and a clinical examination, which included a MOS, sEMG, and 3D pelvic floor ultrasound. The inclusion criteria were 6 to 8 weeks postpartum and the ability to tolerate gynecological examination. Individuals with gynecological bleeding, suspected pregnancy, inability to perform the Valsalva maneuver, and severe medical or surgical diseases were excluded.

2.2. Assessment of PFMS

PFMS was evaluated by a physician according to the MOS. Participants who underwent MOS assessment, and sEMG and 3D pelvic floor ultrasound examinations were all placed in the lithotomy position, and asked to perform PFM contractions (PFMCs) without the abdominal, gluteal, or hip adductor muscles during the corresponding contraction period to ensure that they had mastered the test correctly. PFMS was evaluated according to the following scale: 0, no contraction; 1 (very weak pressure), a barely perceptible contraction lasting <1 second; 2 (weak pressure), a faint contraction persisting 1 to 3 seconds; 3 (moderate pressure), a contraction that resulted in resistance to the elevation of the examiner finger within the vaginal vault and a duration of 4 to 6 seconds; 4 (good pressure), perceptible resistance to the elevation of the finger for a period of 7 to 9 seconds; and 5 (strong pressure), a strong contraction with a duration ≥9 seconds.^[20,21]

2.3. Assessment of pelvic floor sEMG

A Biostimulatory feedback instrument (MLD B2T, Medlander, Najing, Jiangsu, China) and disposable vaginal probe (MLD V1, Medlander, Najing, Jiangsu, China) were used to perform sEMG, including pre-baseline rest, phasic contractions, tonic contractions (TC), endurance contractions, and post-baseline rest, following the Glazer protocols.^[22] A vaginal probe was placed into the vagina of the participants who underwent the test, and 2 electrodes were positioned on either side of the abdominal muscles to monitor unwanted muscle activation. Two other reference electrodes were placed on the bilateral anterior superior iliac spines (Fig. 1). The evaluator instructed patients to perform vaginal contractions, guided by words such as “Please relax your abdomen and hips,” “Please hold in as if you are experiencing an urge to urinate and have a bowel movement at the same time.” The automated protocol software instructed the participants using text hints on a screen and voice prompts. In addition, study staff supervised the participants in performing the contractions correctly. There was a 30 seconds study period before the test to ensure that the participants had mastered the test correctly.

Figure 1.

Position of 4 electrodes.

2.4. Assessment of 3D pelvic floor ultrasound

All ultrasound assessments were performed by an experienced sonographer at the authors’ hospital. Transperineal ultrasound (Reson8s 3D ultrasound system, Mindray Reson8s (11), Shenzhen, Guangdong, China) was used to evaluate pelvic floor morphology. A transducer (D8-2U Resona 8, Shenzhen, Guangdong, China) was placed on the perineum in the midsagittal plane with a sweep angle of 85° at rest, Valsalva, and PFMC. Some guiding words, such as “Please hold in as if you are experiencing an urge to urinate and have a bowel movement at the same time” and “Please inhale deeply and hold your breath, then tense your chest and abdominal muscles and push down as if you are defecating or giving birth” were used for PFMC and Valsalva. At most, 3 Valsalva maneuvers and PFMC were required, with the most effective contraction being used for evaluation. The bladder neck presentation (BNP) (at rest), urethral rotation angle, bladder neck descent (BND), and hiatal area were recorded for further analysis. Negative numbers indicate that the pelvic organs were below the lower margin of the pubic symphysis.

2.5. Statistical analysis

All statistical analyses were performed using SPSS version 26.0 (IBM Corporation, Armonk, NY). Count and measurement data are expressed as n (%) and mean ± standard deviation, respectively. The results were compared and analyzed using one-way analysis of variance (ANOVA) and multivariate analysis between the groups. Possible confounding factors, such as neonatal weight, gestational weight gain (GWG), body mass index, CS, VD, forceps delivery, and number of fetuses, were included as covariates. Differences with a 2-tailed P < .05 were considered to be statistically significant for all tests.

3. Results

In total, 971 participants (primipara 553, deuteripara 361, and tertipara 57) were included in the analysis. Among the participants, age ranged from 19 to 44 years (mean [± standard deviation], 30.84 ± 3.88 years); neonatal weight ranged from 0.77 to 5.95 kg (mean, 3.3 ± 0.45 kg); GWG ranged from 0 to 30 kg (mean, 12.54 ± 4.68 kg); body mass index ranged from 16.8 to 35.63 kg/m² (mean, 23.34 ± 2.82 kg/m²); 128 (13.2%) and 843 (86.8%) had <12 and >12 years of education, respectively; and 124 (12.8%) underwent CS, 803 (82.7%) VD, and 44 (4.5%) forceps delivery. A total of 963 (99.2%) participants had single births and 8 (0.8%) had twin or triplet births. Baseline demographic features are summarized in Table 1.

Table 1.

General characteristics of research participants.

Factors	Group	Number (%)	Mean ± SD (min-max)
Age, yr			30.84 ± 3.88 (19–44)
NW, kg			3.3 ± .45 (0.77–5.95)
GWG, kg			12.54 ± 4.68 (0–30)
BMI			23.34 ± 2.82 (16.8–35.63)
Education, yr	<12	128 (13.2%)
	≥12	843 (86.8%)
DM	CS	124 (12.8%)
	VD	803 (82.7%)
	FD	44 (4.5%)
NOF	1	963 (99.2%)
	≥2	8 (0.8%)

BMI = body mass index, CS = cesarean section, DM = delivery mode, FD = forceps delivery, GWG = gestational weight gain, NOF = number of fetus, NW = neonatal weight, VD = vaginal delivery.

One-way ANOVA indicated that the differences among primipara, deuteripara, and tertipara in pre-baseline rest, phasic contractions, TC, endurance contractions, post-baseline rest, and MOS were not statistically significant (P = .539, P = .169, P = .248, P = .465, P = .659, and P = .385, respectively). Multivariate analysis yielded similar results, except for TC (P = .020), with the TC amplitude of primipara being lower than that of the deuteripara in the post hoc comparison (P = .008). In one-way ANOVA, the differences between primipara, deuteripara, and tertipara in BNP, urethral rotation angle, BND, and hiatal area were statistically significant (P < .001, P = .036, P < .001, and P = .006, respectively). However, only the differences in BNP and BND remained statistically significant after multivariate analysis (P = .002, P = .001, respectively), with BNP in primiparas being greater than that of deuteriparas and tertipara (P = .002, P = .008, respectively), and BND being lower than that of deuteriparas and tertiparas in further post hoc comparisons (P = .002, P = .003, respectively) (Table 2).

Table 2.

One-way analysis of variance (ANOVA) analysis and multivariate analysis of parameters of surface electromyography (sEMG), MOS, and transperineal ultrasound in different parity groups.

Factors	Primipara (n = 553)	Deuteripara (n = 361)	Tertipara (n = 57)	Fone	P one	Fmul	P mul
PreRB, μV	4.84 ± 3.32	4.78 ± 3.18	4.34 ± 2.85	.618	.539	.766	.465
PC, μV	28.81 ± 15.21	30.62 ± 14.99	30.86 ± 14.56	1.781	.169	2.099	.123
TC, μV	19.14 ± 12.00a	20.39 ± 11.01b	19.86 ± 10.27	1.396	.248	3.947	.020
EC, μV	16.36 ± 10.19	17.13 ± 9.18	17.22 ± 9.01	.766	.465	2.694	.068
PostRB, μV	4.11 ± 3.32	4.32 ± 3.36	4.20 ± 3.85	.418	.659	2.560	.078
MOS	1.64 ± 0.94	1.71 ± 0.968	1.56 ± 1.02	.957	.385	.967	.381
BNP, cm	−.13 ± .89b	−.40 ± .89a	−.57 ± 1.09a	13.287	.000	6.323	.002
URA	84.32 ± 28.45	88.04 ± 27.99	92.47 ± 32.31	3.329	.036	1.117	.328
BND, cm	2.84 ± .91a	3.14 ± .92b	3.36 ± 1.05b	16.417	.000	7.075	.001
HA, cm2	20.17 ± 5.54	21.13 ± 6.10	22.25 ± 7.13	5.166	.006	1.476	.229

Post hoc test: a < b < c, one one-way ANOVA analysis.

BND = bladder neck descent, BNP = bladder neck presentation, EC = endurance contraction, HA = hiatal area, MOS = modified Oxford scale, mul = multivariate analysis, PC = phasic contraction, PostBR = post-baseline rest, PreBR = pre-baseline rest, TC = tonic contraction, URA = urethral rotation angle.

4. Discussion

The present study assessed the effects of parity on pelvic floor morphology and function in women during the early postpartum period. Unlike other studies, this study performed a comprehensive evaluation of PFM function using MOS, sEMG, and 3D pelvic floor ultrasonography, thus increasing the accuracy of determining the decline in PFM.

In the present study, we found that almost all sEMG and MOS parameters were not associated with parity. Similar to our findings, other studies have reported that PFM contractility is not impaired when parity increases.^[15,23,24] Although numerous studies have documented the damage caused by pregnancy and delivery to the PFM, its contractility is likely to recover within 1 year after birth.^[25,26] In addition, we found that the differences in TC were statistically significant, with the amplitude of primiparas being lower than that of deuteriparas, which is similar to previously published results.^[27] Such a surprising finding could also be attributed to the body adaptation and self-repair ability rather than the benefits of parity.^[27]

In contrast to the sEMG and MOS results, BNP values decreased, and BND increased as parity increased. Previous studies have reported that parity was condemned for the development of urethral mobility.^[28] Structural deformation of the pelvic floor occurs during pregnancy, and probably remains in VD after delivery in some women, which may have contributed to prolapse of the bladder neck.^[12,29–31] In addition, differences in both BNP and BND were noted between primiparas and multiparas, suggesting that most damage to the pelvic floor occurred during the first delivery, as reported in some previous studies.^[32,33]

5. Limitations

Due to the retrospective design of the study, we could only include existing factors in the analysis and could not include more potential factors, as in a prospective study. The number of multiparas (>3) was too small to observe changes in PFMS or pelvic organ descent when parity continued to increase.

6. Conclusion

Impairment of pelvic floor function was not statistically associated with parity according to the modified Oxford Scale score or surface electromyography. However, parity was significantly correlated with descent of the bladder neck, and most of the effects appeared to occur during the first delivery.

Author contributions

Conceptualization: Jianqi Fang.

Data curation: Ronghua Zhang, Shuqin Lin.

Formal analysis: Jianqi Fang.

Methodology: Juan Lin.

Project administration: Juan Lin, Jinming Shen.

Resources: Ronghua Zhang, Shuqin Lin, Binglan Lai, Yi Chen, Yao Lu, Miao Wang, Yang Lin, Yilin Weng.

Supervision: Juan Lin, Jinming Shen.

Writing – original draft: Jianqi Fang.

Writing – review & editing: Jinming Shen.