Effect of gestational weight gain on postpartum pelvic floor function in twin primiparas: a single-center retrospective study in China

doi:10.21203/rs.3.rs-1806531/v1

Background

The effect of GWG as a controllable factor during pregnancy on pelvic floor function has rarely been investigated, and studies on twin primiparas are even less frequent. The objective of the present study was to explore the correlation between GWG and postpartum pelvic floor function in twin primiparas.

Methods

We retrospectively analyzed the clinical data of 184 twin primiparas in the pelvic floor rehabilitation system of the First Affiliated Hospital of Chongqing Medical University from January 2020 to October 2021. Based on the GWG criteria recommended by the Institute of Medicine, the study subjects were divided into two groups: adequate GWG and excessive GWG. Univariate and multivariate logistic regression models were applied to explore the relationship between GWG and pelvic floor.

Results

Among the 184 twin primiparas, 20 (10.87%) had excessive GWG. The rates of abnormal vaginal dynamic pressure (95% vs 74.39%), severely impaired type I muscle fibers (80% vs 45.73%), anterior vaginal wall prolapse (90% vs 68.90%), and stress urinary incontinence (50% vs 20.12%) of twin primiparas with excessive GWG were significantly higher than those with adequate GWG. There was no significant difference between the total score of the PFDI-20 or the scores of the POPDI-6, CRADI-8, and UDI-6 in the two groups (P > 0.05). After adjusting for potential confounding factors, the results showed that excessive GWG was positively associated with abnormal vaginal dynamic pressure (OR = 8.038, 95% CI: 1.001–64.514), severely impaired type I muscle fibers (OR = 8.654, 95% CI: 2.462–30.416), anterior vaginal wall prolapse (OR = 4.705, 95% CI: 1.004–22.054), and stress urinary incontinence (OR = 4.424, 95% CI: 1.578–12.403).

Conclusion

Excessive GWG in twin primiparas was positively correlated with the prevalence of pelvic floor dysfunction, which did not exacerbate pelvic floor symptoms in twin primiparas. Reasonable control of GWG is beneficial in reducing the risk of abnormal pelvic floor function. Therefore, individualized management for twin pregnancies, providing healthy lifestyle guidance, and promoting weight management should be an important part of perinatal care.

twins

primiparas

pelvic floor function

gestational weight gain

GWG

In recent decades, the global rate of twin birth has been rising due to the delay of female childbearing age and the popularization of assisted reproductive technology [1]. Between 2012 and 2020, the birth rate of twins increased in China [2]. Compared with singletons, the incidence of postpartum pelvic floor injury and pelvic floor disorder (PFDs) is more significant in twin pregnant women[3, 4]. PFDs include pelvic organ prolapse (POP) and urinary incontinence (UI) [5], which are public health challenges for women worldwide and negatively affect the lives of millions of adult women [6–8]. The effect of weight factors on pelvic floor function has been a hot topic. Most studies have focused on the effects of maternal prepregnancy BMI and newborn birthweight on pelvic floor function [9–11], and few studies have explored the effects of GWG as a controllable factor during pregnancy on pelvic floor function. A systematic review and meta-analysis showed that excessive GWG is one of the risk factors for PFDs [12], and this limited study did not address the twin primiparas group.

With the increase in gestational age, GWG is a normal physiological process of pregnancy development [13]. Adequate GWG can reduce the incidence of maternal and neonatal complications [14–16]. In 2009, the Institute of Medicine (IOM) published GMG guidelines and developed different criteria for GWG of singleton and twin pregnant women to promote GWG control in the normal range [17]. However, excessive GWG is becoming increasingly prevalent. A systematic review and meta-analysis that included more than one million pregnant women reported that approximately 51% of pregnant women gained more weight during pregnancy compared to the IOM recommendation [18]. Several studies from different regions of China have also found that more than 30% of Chinese women gained more GWG than the IOM criteria in the third trimester [19–22].

Compared to singleton pregnancies, twin pregnancies have more GWG due to the variability in the fetal number and physiological changes during pregnancy [17]. Based on this, we derived the following hypothesis: GWG of twin pregnancies excessively increases the risk of postpartum PFDs. This retrospective study explored the relationship between GWG and pelvic floor function of twin primiparas to provide clinical evidence for weight management of twin pregnant women, promote scientific nutrition intake during pregnancy, achieve adequate GWG, and reduce the negative impact on the pelvic floor.

Study Subjects

This study reviewed the postpartum pelvic floor function data of twin mothers in the postpartum pelvic floor rehabilitation system of the First Affiliated Hospital of Chongqing Medical University from January 2020 to October 2021. After matching with the electronic medical record system, according to the inclusion and exclusion criteria, 184 twin primiparas were finally included in the study. The inclusion criteria were twin primiparas with gestational weeks ≥ 34 weeks who were delivered in this hospital. Excluded subjects were those who failed to match the postpartum pelvic floor rehabilitation system and the electronic medical record system, multiparas, and those with PFDs symptoms before and during pregnancy. Since the IOM does not develop GWG criteria for twin pregnancies with prepregnancy underweight (body mass index [BMI] < 18.5), this group was excluded.

The 2009 IOM guidelines recommend that the normal range of GWG is 16.8–24.5 kg for twin pregnancies with normal prepregnancy BMI (BMI 18.5–24.9 kg/m²), 14.1–22.7 kg for those who were prepregnancy overweight (BMI 25-29.9 kg/m²), and 11.3–19.1 kg for those who were prepregnancy obese (BMI ≥ 30 kg/m²). These three groups were judged to have excessive GMG when their GWG exceeded 24.5, 22.7, and 19.1 kg, respectively. As there were no sample data with insufficient GWG in this study, the subjects were divided into two groups: adequate GWG and excessive GWG for analysis.

The study meets the ethical guidelines of the Helsinki Declaration and has been reviewed and approved by the Ethics Committee of the First Affiliated Hospital of Chongqing Medical University (2019 − 239). As a retrospective study, the Ethics Committee of the First Affiliated Hospital of Chongqing Medical University approved the exemption of informed consent, and the datasets were anonymized before their use.

Data collection

The postpartum pelvic floor rehabilitation system recorded maternal data who returned to the hospital for pelvic floor function examination after 6 weeks of delivery, including general maternal information, abdominopelvic pressure values measured by the instrument, POP results measured by the pelvic organ prolapse quantification (POP-Q) system, and the data filled in the Pelvic Floor Distress Inventory-Short Form 20 (PFDI-20). The electronic medical record system includes demographic data and obstetric clinical data. The information in the two databases was matched by “hospitalization number (unique identity)” using the VLOOKUP function in Excel 2019.

Outcome assessment

The dynamic pressure value of the maximum vaginal contraction of the mother was measured by a vaginal balloon pressure probe; 80–150 cm H₂O was normal, and < 80 cm H₂O was abnormal.

Pelvic floor muscle strength was tested by trained and fixed examiners through a neuromuscular stimulation therapy instrument. Type I muscle fiber strength refers to the time that a muscle contraction can last with an intensity of more than 40% of its maximum value, divided into 0-V, sustained 0 s for level 0, sustained 1 s for level I, and so on, sustained 5 s and above for level V. Type II muscle fiber strength refers to the number of repeatable times when the maximum strength of muscle contraction reaches more than 60%, divided into 0-V, sustained 0 times as level 0, sustained 1 times as level I, and so on, sustained 5 times and above as level V. Combined with previous literature and clinical practice, muscle strength level 0-II was defined as severely damaged pelvic floor muscle fibers for analysis.

POP is divided into anterior vaginal wall prolapse, apical vaginal prolapse (uterine prolapse), and posterior vaginal wall prolapse [23]. The objective diagnosis of POP is based on the evaluation results of the POP-Q, which is performed by a standardized trained pelvic floor rehabilitation therapist according to a joint commission of the International Urogynecological Association and the International Continence Society norms [24]. The hymen was taken as the fixed anatomical reference point in the POP-Q system, and its plane was defined as zero. Six measurement points: points Aa and Ba are the anterior vaginal wall sites, points C and D are the apical vaginal sites, and points Ap and Bp are the posterior vaginal wall sites. The anatomical position of the measuring point is negative above or near the hymen and positive below or distal. The examinee empties the bladder, assumes a supine position, completes the Valsalva maneuver, and performs the examination when the maximum prolapse is reached. The values of the Aa point or Ba point > -3 were diagnosed as anterior vaginal wall prolapse, C or D point > 2 - total vaginal length was diagnosed as apical vaginal prolapse or uterine prolapse, and Ap or Bp point > -3 was diagnosed as posterior vaginal wall prolapse.

In this study, we adopted the validated Chinese version of the PFDI-20 questionnaire to investigate the effect of PFDs on the quality of life of postpartum women [25]. The PFDI-20 questionnaire is divided into three subscales: the Pelvic Organ Prolapse Distress Inventory 6 (POPDI-6), the Colorectal-Anal Distress Inventory 8 (CRADI-8), and the Urinary Distress Inventory 6 (UDI-6). The total score of the three subscales was 0-300. The higher the score, the more severe the symptoms of PFDs, and the greater the impact on maternal quality of life.

The existence of any type of UI is determined based on an affirmative answer to the Urinary Distress Inventory. For the entry "Do you usually experience urine leakage associated with a feeling of urgency, that is, a strong sensation of needing to go to the bathroom?" answered "Yes", and the diagnosis was urgent urinary incontinence (UUI). For the entry "Do you usually experience urine leakage related to coughing, sneezing, or laughing?" answered "Yes", and the diagnosis was stress urinary incontinence (SUI). The diagnosis of mixed urinary incontinence (MUI) was made by answering "yes" to the above two questions.

Covariates

Through literature references, the covariates of this study included maternal demographic characteristics (age, prepregnancy BMI, education level, and place of residence), relevant surgical history (pelvic and abdominal surgery, in vitro fertilization and embryo transfer [IVF-ET], cervical surgery), and obstetric clinical conditions (number of pregnancies, total birth weight of newborns, mode of delivery). Pelvic and abdominal surgery included appendectomy, adnexectomy, ovarian cystectomy, salpingotomy, myomectomy, and teratoma stripping. Cervical surgery included cervical conization and cervical polypectomy.

Statistical analyses

The data were analyzed and processed by SAS 9.4 software. Means ± standard deviations were used to describe normally distributed measures, and two independent samples t test was used to compare the groups (adequate/excessive); median and interquartile range were used to describe measures of skewed distributions, and the Wilcoxon rank-sum test was used for comparison between the groups; the number of cases (n) and rates were used to describe the count data, and the χ² test or Fisher's exact test was used to compare between the groups. Exploring the correlation between abnormal pelvic floor function and excessive GWG by the multivariate logistic regression model. Two-sided P < 0.05 was considered statistically significant.

The maternal data of 412 twin pregnancies in the postpartum pelvic floor rehabilitation system were extracted from January 2020 to October 2021. We excluded 39 cases whose electronic medical record system could not match, 72 cases of multiparas, 45 cases of delivery under 34 weeks, 65 cases of PFDs symptoms before and during pregnancy, and 7 cases of prepregnancy underweight. Finally, 184 cases of twin primiparas were included for analysis, including 164 in the adequate GWG group and 20 in the excessive GWG group (Fig. 1).

The basic characteristics and risk factors for the study population are shown in Table 1. The adequate GWG group included 164 (89.1%) subjects, with a mean age of 30.3 ± 3.87 years; the excessive GWG group included 20 (10.9%) subjects, with a mean age of 29.1 ± 4.44 years. There was no statistically significant difference between the two groups in terms of age, prepregnancy BMI, place of residence, history of pelvic and abdominal surgery, history of IVF-ET surgery, cervical surgery, number of pregnancies, gestational week at delivery, total birthweight of the newborns, or delivery mode (P > 0.05). BMI at delivery and GWG were higher in twin primiparas with excessive GMG than in twin primiparas with adequate GMG, and the difference was statistically significant (P < 0.05).

Table 1

Basic and clinical characteristics of the study population
Characteristic	Total (n = 184)	Adequate GWG (n = 164)	Excessive GWG (n = 20)	χ2/t/Z	P value
Baseline demographic
Age (years)	30.17 ± 3.94	30.30 ± 3.87	29.10 ± 4.44	1.288	0.199
prepregnancy BMI (kg/m²)	21.53 ± 2.55	21.61 ± 2.60	20.82 ± 2.00	1.322	0.188
Education				0.043	0.979
Middle school and less	17 (9.24%)	15 (9.15%)	2 (10.00%)
High and secondary school	68 (36.96%)	61 (37.20%)	7 (35.00%)
College and higher	99 (53.80%)	88 (53.66%)	11 (55.00%)
Residence				—	> 0.999
Rural	22 (11.96%)	20 (12.20%)	2 (10.00%)
Urban	162 (88.04%)	144 (87.80%)	18 (90.00%)
Relevant surgical history
Pelvic or abdominal surgery				—	> 0.999
No	143 (77.72%)	127 (77.44%)	16 (80.00%)
Yes	41 (22.28%)	37 (22.56%)	4 (20.00%)
IVF-ET				1.876	0.171
No	93 (50.54%)	80 (48.78%)	13 (65.00%)
Yes	91 (49.46%)	84 (51.22%)	7 (35.00%)
cervical surgery				—	> 0.999
No	179 (97.28%)	159 (96.95%)	20 (100.00%)
Yes	5 (2.72%)	5 (3.05%)	0 (0.00%)
Obstetrical clinical features
Pregnancies	2 (1,2)	2 (1,2)	1.5 (1,2)	0.173	0.863
Gestation (weeks)	37 (36.14,37.5)	37(36.14,37.43)	37.43(36.21,37.71)	1.664	0.096
Total birthweight (g)	5106.45 ± 599.58	5080.24 ± 563.14	5321.3 ± 829.03	-1.265	0.22
BMI at delivery (kg/m²)	28.41 ± 2.92	28.06 ± 2.76	31.28 ± 2.62	-4.947	< 0.001
GWG (kg)	17.6 ± 5.49	16.46 ± 4.55	26.95 ± 3.07	-13.568	< 0.001
Delivery mode				—	> 0.999
Cesarean delivery	182 (98.91%)	162 (98.78%)	20 (100.00%)
Vaginal delivery	2 (1.09%)	2 (1.22%)	0 (0.00%)
Abbreviations: BMI Body mass index, GWG Gestational weight gain, IVF-ET In vitro fertilization and embryo transfer. P < 0.05 are highlighted in bold text.

Postpartum dynamic vaginal pressure abnormalities were found in 76.63% of twin primiparas, 49.46% of the study subjects had severe damage to type I muscle < fibers, 71.2% had anterior vaginal wall prolapse, and the prevalence of urinary incontinence was 30.97%. Univariate analysis showed that the incidence of SUI, abnormal vaginal dynamic pressure, severe damage of type I muscle fibers, and anterior vaginal wall prolapse in the excessive GWG group were significantly higher than those in the adequate GWG group, P < 0.05 (Table 2).

Table 2

The relationship between GWG and pelvic floor function
Variable	Total (n = 184)	Adequate GWG (n = 164)	Excessive GWG (n = 20)	P value
Abnormal vaginal dynamic pressure	141 (76.63%)	122 (74.39%)	19 (95.00%)	0.048
Severely impaired muscle fibers
type Ⅰ	91 (49.46%)	75 (45.73%)	16 (80.00%)	0.004
type Ⅱ	116 (63.04%)	100 (60.98%)	16 (80.00%)	0.096
Pelvic organ prolapse
Anterior vaginal wall prolapse	131 (71.20%)	113 (68.90%)	18 (90.00%)	0.049
Apical vaginal prolapse	34 (18.48%)	30 (18.29%)	4 (20.00%)	0.768
Posterior vaginal wall prolapse	30 (16.30%)	26 (15.85%)	4 (20.00%)	0.748
Urinary incontinence
stress urinary incontinence	43 (23.37%)	33 (20.12%)	10 (50.00%)	0.009
Urgent urinary incontinence	25 (13.59%)	22 (13.41%)	3 (15.00%)	0.739
Mixed urinary incontinence	11 (5.98%)	10 (6.10%)	1 (5.00%)	0.999
Abbreviations: GWG Gestational weight gain. P < 0.05 are highlighted in bold text.

Table 3 shows that the mean PFDI-20 score was 15.14 ± 23.90 in the group with adequate GWG and 14.01 ± 14.77 in the group with excessive GWG. There were no significant differences between the total score of the PFDI-20 and the scores of the subscales POPDI-6, CRADI-8, and UDI-6 in the two groups (P > 0.05). Figure 2 describes the distribution of the total PFDI-20 scores and the scores of each subscale for both adequate GWG and excessive GWG subjects. The distributions of the PFDI-20 and its subscale scores were very similar.

Table 3

The Correlation between GWG and PFDI-20
Variable	Total (n = 184)	Adequate GWG (n = 164)	Excessive GWG (n = 20)	t value	P value
POPDI-6	4.46 ± 8.69	4.47 ± 8.74	4.38 ± 8.49	0.047	0.963
CRADI-8	3.99 ± 8.11	4.12 ± 8.46	2.97 ± 4.24	0.994	0.326
UDI-6	6.57 ± 11.13	6.55 ± 11.24	6.67 ± 10.42	-0.042	0.966
PFDI-20	15.02 ± 23.06	15.14 ± 23.90	14.01 ± 14.77	0.298	0.767
Abbreviations: PFDI-20, Pelvic Floor Distress Inventory - Short Form 20; POPDI-6, Pelvic Organ Prolapse Distress Inventory 6; CRADI-8, Colorectal Anal Distress Inventory 8; UDI-6, Urinary Distress Inventory 6.

A multivariate logistic regression model was used to explore the relationship between excessive GWG and pelvic floor dysfunction. Table 4 shows that after adjusting for age, prepregnancy BMI, education level, and place of residence, excessive GWG was significantly and positively correlated with abnormal vaginal dynamic pressure (OR = 8.128, 95% CI: 1.024–64.517), severe impairment of type I muscle fibers (OR = 7.153, 95% CI: 2.124–24.087), anterior vaginal wall prolapse (OR = 5.343, 95% CI: 1.152–24.778), and SUI (OR = 4.943, 95% CI: 1.800-13.577). Even after adding the relevant surgical history (pelvic and abdominal surgery, IVF-ET, cervical surgery) and obstetrical risk factors (number of pregnancies, total birthweight of newborns, delivery mode) into the regression model, abnormal dynamic vaginal pressure (OR = 8.038, 95% CI: 1.001–64.514), severe damage to type I muscle fibers (OR = 8.654, 95% CI: 2.462–30.416), anterior vaginal wall prolapse (OR = 4.705, 95% CI: 1.004–22.054), and SUI (OR = 4.424, 95% CI: 1.578–12.403) were still associated with excessive GWG.

Table 4

Results of multivariate logistic regression analysis of excessive GWG and abnormal pelvic floor function
dependent variable	β	SE	Wald χ2	P value	OR (95% CI)
Model 1^a
Abnormal vaginal dynamic pressure	2.095	1.057	3.930	0.047	8.128 (1.024, 64.517)
Severe impairment of type I muscle fibers	1.967	0.619	10.087	0.001	7.153 (2.124, 24.087)
anterior vaginal wall prolapse	1.676	0.783	4.583	0.032	5.343 (1.152, 24.778)
stress urinary incontinence	1.598	0.516	9.609	0.002	4.943 (1.800, 13.577)
Model 2^b
Abnormal vaginal dynamic pressure	2.097	1.058	3.928	0.047	8.144 (1.023, 64.814)
Severe impairment of type I muscle fibers	1.964	0.620	10.029	0.002	7.127 (2.114, 24.028)
anterior vaginal wall prolapse	1.615	0.785	4.232	0.040	5.030 (1.079, 23.440)
stress urinary incontinence	1.514	0.522	8.426	0.004	4.546 (1.635, 12.638)
Model 3^c
Abnormal vaginal dynamic pressure	2.084	1.063	3.847	0.049	8.038 (1.001, 64.514)
Severe impairment of type I muscle fibers	2.158	0.641	11.325	0.001	8.654 (2.462, 30.416)
anterior vaginal wall prolapse	1.549	0.788	3.860	0.049	4.705 (1.004, 22.054)
stress urinary incontinence	1.487	0.526	7.996	0.005	4.424 (1.578, 12.403)
Abbreviations: GWG Gestational weight gain. Independent variable is excessive GWG. P < 0.05 are highlighted in bold text. ^a Adjusted for age, prepregnancy BMI, education level, and place of residence. ^b On the basis of Model 1, add pelvic and abdominal surgery, IVF-ET, cervical surgery. ^c On the basis of Model 2, add the number of pregnancies, the total weight of newborns, delivery mode.

Pelvic floor muscle fibers are divided into two types: type I muscle fibers (slow muscle fibers) and type II muscle fibers (fast muscle fibers) [26]. The interaction among pelvic floor muscles, fascia, and ligaments is essential to support the normal physiological state and function of pelvic organs [27]. Damage to the pelvic floor muscle fibers can lead to structural defects and dysfunction of the pelvic floor, which in turn can lead to postpartum UI and POP [28–31]. We found that abnormal postpartum vaginal dynamic pressure and injuries to the pelvic floor type I and II muscle fibers were common phenomena in the twin pregnancy population regardless of whether GWG was adequate or excessive. Excessive GWG further increased the risk of pelvic floor muscle damage, with a high rate of abnormal vaginal dynamic pressure of 95% (19/20) and severely damaged postpartum type I muscle fibers of 80% (16/20) in this group.

This study also found that, just as there was a higher proportion of abnormal dynamic vaginal pressure and severe damage to type I muscle fibers in the excessive GWG group, there was also a higher incidence of postpartum anterior vaginal wall prolapse and SUI in this group, the mechanism of which may be related to pelvic floor muscle damage due to excessive GWG [32]. During pregnancy, in the absence of pathological edema such as preeclampsia, heart failure, or nephropathy, excessive GWG is mainly associated with excessive maternal fat gain [13]. Excessive fat accumulation can create increasing and continuous pressure on the pelvic floor muscles and bladder, resulting in increased intra-abdominal pressure, leading to weakening of the pelvic floor muscle strength and destruction of fascia, causing damage to ligaments, nerves, blood vessels, and other tissues, thus changing the normal structure and anatomical position of the urethra and bladder and causing them to lose their original support, which are the pathophysiological reasons for the occurrence of POP and SUI [33–35].

We found that the prevalence of postpartum anterior vaginal wall prolapse in twin primipara was 71.20% by the POP-Q examination, and the rate was as high as 90% in the group with excessive GWG. The occurrence of anterior vaginal wall prolapse was significantly associated with excessive GWG (OR = 4.705, 95% CI: 1.004–22.054). A review of the literature by Lee [33] found that the prevalence of POP showed an increasing trend with increasing BMI. A randomized double-blind study [36] investigated 16608 women and found that POP progressed with weight gain, but prolapse did not improve with weight loss. Another randomized controlled study of overweight/obese women assessed subjects by the POP-Q system and reached the same conclusion [37]. These findings may indicate that the pelvic floor damage caused by excessive weight gain is irreversible. From this, we can infer that preventing excessive GWG and keeping GWG within reasonable limits may reduce the occurrence of irreversible POP.

UI is a common disease that affects women's quality of life. SUI, UUI, and MUI are the main types, among which SUI is most common in postpartum women [38]. The results of this study showed that the incidence of postpartum SUI, UUI and MUI in twin primiparas was 23.37%, 13.59%, and 5.98%, respectively, which was similar to the findings of a prospective longitudinal study conducted by KarenNg et al on singleton women [39]. We also found that SUI occurred in up to 50% (10/20) of twin primiparous women in the excessive GWG group, which was significantly higher than that in the group with suitable GWG (P < 0.009). The prevalence of SUI was significantly positively correlated with GWG excess (OR = 4.424, 95% CI: 1.578–12.403). A systematic review and meta-analysis that included 46 studies with 73010 subjects came to a similar conclusion: excessive GWG was associated with postpartum SUI [12]. We thus speculated that excessive GWG may play an etiological role in the development of SUI in twin primiparas.

Some studies have reported that the prevalence of postpartum SUI gradually decreases over time [40, 41]. Possibly due to differences in study populations and follow-up time, more studies have found the opposite: the effects of postpartum SUI on women's health are sustained, and over time, the cumulative incidence of SUI increases significantly [39, 42–46]. Other studies have found that the persistence of postpartum SUI is caused by higher BMI and excessive GWG in pregnant women [14, 39, 47, 48]. From these results, it is clear that control of excessive GWG is essential for the prevention of postpartum SUI. Preventive care for SUI should be provided throughout the life span of adult females, in addition to covering pregnancy and the puerperium period.

A study assessing the correlation between obesity and POP symptoms in Korean women found no significant correlation between obesity and the severity of POP symptoms [49]. This finding corroborates our results. This study found that although excessive GWG increased the prevalence of PFDs, it did not further exacerbate pelvic floor symptoms in twin primiparas. This may be related to the small sample size of the excessive GWG group in this study and may be the reason why the effect of excessive GWG on pelvic floor symptoms no longer increases after reaching a critical threshold level. The results of this study remind us that although excessive GWG does not exacerbate pelvic floor symptoms, pelvic floor injury and anatomical changes have occurred, and the negative impact of excessive GWG on the pelvic floor should not be overlooked as a result.

Although the birth rate of twins has increased significantly in recent decades, access to the sample is still limited compared to that of singletons. The above study sample was only from one tertiary teaching hospital in China, and there is still a need for a multicenter, large sample study to minimize bias. In assessing the effect of GWG on pelvic floor function, we only focused on the total growth of GWG and did not pay attention to the effect of the rate of weight gain at different periods of pregnancy. Additionally, this study did not explore postpartum pelvic floor function in the prepregnancy underweight and insufficient GWG groups, which will be the direction of follow-up research. The present study on the relationship between excessive GWG and pelvic floor function in twin primiparas is retrospective, and the argument for causality needs to be further confirmed by prospective cohort studies and randomized controlled trials.

The results of this study showed that excessive GWG was positively associated with postpartum pelvic floor muscle impairment, anterior vaginal wall prolapse, and SUI in twin primiparous women, which is independent of other risk factors. Different from immutable factors such as age and race, GWG is a critical variable in prenatal care management because it is one of the few changeable factors affecting pelvic floor function. Prevention of excessive GWG is increasingly important for prenatal care providers and the functional health of the pregnant woman's pelvic floor.

In view of this, the adoption of individualized management strategies, the provision of effective behavioral counseling and interventions, and the encouragement of active participation of pregnant women in the process of pregnancy weight management should be important components of pregnancy health care services for twin pregnancies. Through scientific weight management during pregnancy, it is important to help pregnant women control GWG within an adequate range to prevent and reduce the occurrence of postpartum PFDs.

GWG: Gestational weight gain; PFDs: Postpartum pelvic floor disorder; POP: Pelvic organ prolapse; UI: Urinaryincontinence; IOM: Institute of Medicine; BMI: Body mass index; POP–Q: Pelvic organ prolapse quantification; PFDI-20: Pelvic floor distress inventory-short form 20; POPDI-6: Pelvic organ prolapse distress inventory 6; CRADI-8: Colorectal anal distress inventory 8; UDI-6: Urinary distress inventory 6; UUI: Urgent urinary incontinence; SUI: Stress urinary incontinence; MUI: Mixed urinary incontinence; IVF-ET: In vitro fertilization and embryo transfer.

Acknowledgments

We recognize the Pelvic Floor Rehabilitation Center of the First Affiliated Hospital of Chongqing Medical University for its contribution to this study and the staff who supported the data collection process of this study.

Authors’ contributions

YZ conceptualized and designed the study, matched the data, interpreted the data, and drafted the manuscript. YT L participated in the study design, performed the statistical analysis, and helped revise the manuscript. JY X collected the data. QR Z, as a pelvic floor rehabilitation examiner, contributed to data acquisition. SY T helped revise the manuscript. BZ L was responsible for the conception and revision. All authors read and approved the final manuscript.

Funding

This study was supported by the National Natural Science Foundation of China (81971406) and the Nursing Research Fund of the First Affiliated Hospital of Chongqing Medical University (HLJJ2018-01)

Availability of data and materials

The datasets used and analyzed during the current study are available from the corresponding author on reasonable request.

Ethics approval and consent to participate

The study meets the ethical guidelines of the Helsinki Declaration and has been reviewed and approved by the Ethics Committee of the First Affiliated Hospital of Chongqing Medical University (2019-239). As a retrospective study, the Ethics Committee of the First Affiliated Hospital of Chongqing Medical University approved the exemption of informed consent, and the datasets were anonymized before their use.

Consent for publication

Not applicable.

Competing interests

The authors declare that they have no competing interests.

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No competing interests reported.

Effect of gestational weight gain on postpartum pelvic floor function in twin primiparas: a single-center retrospective study in China

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