The influence of the menstrual cup on female pelvic floor muscles variables: a prospective case series

ABSTRACT

The aim was to assess and report the effects of menstrual cup on pelvic floor muscles (PFM) function and tone, as well as check the acceptability after a period of three menstrual cycles in healthy young women. The data collected in assessments and reassessments included the International Consultation on Incontinence Questionnaire – Vaginal Symptoms (ICIQ-VS) questionnaire, evaluation of PFM function through PERFECT Scheme, PFM muscle tone, and PFM manometry (Peritron 9300®). A diary regarding the overall colletor acceptability and satisfaction was collected. Ten healthy young women completed the study. There was an improvement in the mean values of maximal voluntary contraction (MVC) (p = 0.032), a decrease in the vaginal resting pressure (VRP) (p = 0.05), and an increase in the number of repetitions of sustained muscle contractions (p = 0.042). Seven women reported some discomfort while using the vaginal cup only in the first cycle while three revealed discomfort during the whole experiment. This study provides preliminary case-based evidence that the use of the vaginal cup for a period of three menstrual cycles changes the VRP, MVC, and PFM tone, as well as improves the repetitions of PFM assessed by digital palpation. Moreover, the women reported the use of vaginal cup as a positive experience.

KEYWORDS:

• Feminine hygiene products
• menstrual cup
• muscle function
• muscle tone
• pelvic floor muscles

Introduction

Nowadays, women have chosen the menstrual cup to replace tampons or pads. The menstrual cup is a reusable silicone bell-shaped intravaginal device that collects menstrual fluid. To insert and remove the cup, users must separate the vaginal walls, but it is also important to relax the muscles surrounding the vagina. According to the manufacturers, women with a high cervix may have more difficulty during these maneuvers. Also, they may find themselves straining to push the cup for removal, which, in the long term, can overload and stretch the pelvic floor muscles (PFM). To avoid that, women should release the vacuum of the menstrual cup before removal, as pointed out by Seale et al. (2019). The FDA reported pain during its use or on removal, irritation, and one case of pelvic pain and urinary incontinence (Gharacheh et al. 2021; FDA 2022).

Hypertonic PFM may contain myofascial trigger points (Zermann et al. 1999) which are often clinically associated with spontaneous pain (Shah et al. 2015). The International Urogynecological Association (IUGA)/International Continence Society (ICS) defines hypertonic PFM as the ones having increased tone related to the contractile or viscoelastic components that can be associated with either elevated contractile activity and/or muscle passive stiffness (Bø et al. 2017). Women with hypertonic PFM may have an increased vaginal resting pressure (VRP), which may lead to pelvic pain (Butrick 2009). In this sense, maybe women with non-relaxing or hypertonic PFM may be the ones experiencing difficulty or pain while inserting or removing the menstrual cup.

Hypertonicity of the PFM has been difficult to assess and quantify, and there are no normative values to diagnose it (Bø et al. 2017). VRP and resting surface EMG have been suggested as methods of assessing this condition (Naess and Bø 2018). Since the menstrual cup remains in the vaginal canal through vacuum, can provide a stretch stimulus by putting constant pressure on the vagina walls, and we hypothesize weather it can promote PFM relaxation in long term. As far as we know, the published studies focused only on safety and acceptability issues (Beksinska et al. 2015; van Eijk et al. 2019). In that sense, this preliminary prospective case series study aimed to report the effects of menstrual cup in PFM function and tone, as well as check the acceptability after a period of three menstrual cycles in healthy women.

Methods

Study design and participants

This was a prospective case series study conducted from July 2020 to December 2020 at the Biomechanics Laboratory of the Health and Sports Science Center – CEFID/Santa Catarina State University (UDESC). The research was carried out according to the Declaration of Helsinki and the Human Research Ethics Committee of UDESC approved the study (number: 3.615.810).

Participants were recruited through posters divulgations, social networks, and pamphlets. This study included nulliparous women over 18 years old, in the reproductive phase, with regular menstrual cycle, who were willing to try using the menstrual cup. Women with history of pelvic surgery; presence prolapse grade III or IV according to pelvic organ prolapse quantification (POP-Q) system; currently having or being treated to urinary tract infection and/or under treatment for any gynecological disease; who already used the menstrual cup; those that did not adapt to use the menstrual cup were excluded.

Selected women were invited to a face-to-face interview to sign the informed consent form and were asked to answer specific questionnaires and perform the physical evaluation.

Intervention

The protocol comprises a period of three menstrual cycles using the menstrual cup.

The participants completed a survey designed by the authors, containing sociodemographic information, anthropometric data, medical history (previous surgeries, current medication), gynecological data (menstrual flow, genital pain, sexual activity, symptoms of urinary tract infection), and attended an individual assessment with a physiotherapist.

Each participant received a menstrual cup kit and was asked to use it for three menstrual cycles. In this study, was used the Violeta Cup®, made of hypoallergenic flexible silicone with 40 mm wide and 55 mm of high. It should be positioned into the vaginal cavity at the beginning of the menstrual cycle and may remain for 8–12 consecutive hours without emptying (Stewart, Greer, and Powell 2010). The instructions for positioning and use were as recommended by the manufacturers. During the menstrual cycle, participants kept a diary detailing the number of days used and tracked episodes of vaginal irritation, general discomfort to use or remove the menstrual cup, as well as leakage episodes.

Outcome assessment

Participants were assessed pre- and post- three menstrual cycles using the menstrual cup. The data collected included International Consultation on Incontinence Questionnaire – Vaginal Symptoms (ICIQ-VS) questionnaire; evaluation of PFM function, including muscle tone; PERFECT Scheme; and PFM manometry. Moreover, a diary regarding the overall acceptability and satisfaction of the menstrual cup was collected.

Primary outcome

The same physiotherapist with more than 15 years of clinical experience working with patients with pelvic floor dysfunction did all the clinical assessments. All volunteers were instructed to assume a modified lithotomy position, and the external and internal genitalia were inspected for abnormalities. The ones who were unable to contract or relax their PFM were first instructed how to do it while receiving feedback during digital palpation.

Pelvic floor muscle tone

Tone is defined by its resting tension, clinically determined by resistance to passive movement (Bø et al., 2017; Frawley et al. 2021). Muscle resting tone was assessed during vaginal examination. We used the digital vaginal palpation method, where the therapist presses the puborectal muscle bellies to the right and left sides (7 o’clock and 5 o’clock positions) after three PFM voluntary contraction. Muscle tone was classified as low (hypotonic), normal, or increased (hypertonic), as suggested by Vieira et al. (2020).

Pelvic floor muscle function

Muscle function refers to the physiological functions of muscles, such as strength and endurance (World Health Organization 2001). According to the PERFECT Scheme, proposed by Laycock and Jerwood (2001), PFM strength was assessed via bidigital palpation on the vaginal canal, and women were asked to perform a maximal voluntary contraction (MVC), as measured by the Modified Oxford Grading Scale. Muscle strength was scaled from 0 to 5, where 0 – no pressure and 5 – strong contraction. The PERFECT Scheme assesses muscle contraction capacity: P for Power (measured by the Modified Oxford Grading Scale); E for Endurance (time holding MVC, up to 10 s); R for Repetitions (how many MVC women can hold, with a rest between them, up to 10 reps); and F for the ability to perform 1-sec MVC (up to 10 reps). Contraction of accessory muscles (abdominals, gluteus, hip adductors) was avoided.

Afterward, VRP and MVC were also assessed by means of precision digital manometer Peritron 9300® (Frawley et al. 2006). For that purpose, vaginal probe was wrapped by a male condom with lubricating gel, and then inserted deflated into the vaginal canal for 3–4 cm from the introitus. Women were instructed to relax their PFM, so that VRP could be recorded. Finally, the device was set to zero, and the MVC was measured. Participants were instructed on how to perform PFM contraction in the same way for manual and manometer assessments. In either the assessments, three repetitions of MVC were made, with an interval of 15 s between them, and the highest score/value was recorded (Frawley et al. 2006).

Secondary outcome

Vaginal symptoms

We applied the ICIQ-VS questionnaire for this purpose. It consists of fourteen questions, divided into three categories: vaginal symptoms subscale (VSS) – ranging from 0 to 53; sexual matters subscale (SMS) – from 0 to 58; and overall impact on quality-of-life subscale (OQOL) – from 0 to 10. Higher scores represent increased severity of symptoms (Tamanini et al. 2008).

Diary of menstrual cup

Participants recorded on a diary the days using the menstrual cup in each cycle, as well as a “yes or no” answer to the following questions: Did you have episodes of vaginal irritation? Did you have leakages? Did you feel any discomfort when removing the menstrual cup? and Did you have discomfort during the use of the menstrual cup? In this last question, if the answer was “yes” women should also report if the discomfort was during the first or in all cycles. They also reported their satisfaction with the menstrual cup with a “yes or no” answer, and whether they would continue to use it after completing the study.

Statistical analysis

Descriptive data were analyzed using the mean and standard deviation, median and interquartile interval, and absolute and relative frequencies of the studied sample variables. SPSS program version 22.0 was used for statistical analyses. The statistical methods employed included Wilcoxon signed-rank test to compare initial and follow-up evaluation of the PERFECT Scheme, MVC and VRP values from manometry and the scores of the each ICIQ-VS subscale. The level of significance was set at 5 percent. The sample size was not calculated a priori. We have a posteriori calculated the Effect Size and Power of the variables that best portray the differences in the Primary Outcomes, the PFM variables which showed some difference between the two clinical sessions.

Results

The initial sample consisted of twenty-five women. Potential participants were twenty-one women, who came to be enrolled in study. Eleven potential participants were not included (five gave up participating, four sought us after the collection had already started, and two gave up using the cup due to difficulty in adaptation), resulting in a final sample of ten women. None of them used IUD as a contraceptive method, as recent evidence suggests that it may be dislodged by the menstrual cup, if not correctly used (Jill et al. 2020). Seven of the ten participants try to include 1 or 2 h of physical activity in their weekly routines, namely gym, walking, swimming, or Pilates, which may be considered as residual and cannot be considered a factor influencing the results.

Table 1 presents the sociodemographic characteristics of the twelve participants initially evaluated. Their mean age was 24.3 ± 2.6 years, all single and sexually active, with a prevalence of 75 percent white women and the majority was classified as eutrophic. The majority (83.3 percent) of the participants reported absence of urinary tract infections; 25 percent of the women mentioned constipation. Regarding contraceptive use, 50 percent of participants reported taking oral contraceptive pills from different brands, 8.3 percent the vaginal ring, and 41.7 percent declared not using contraception.

Table 1. Sociodemographic characterics of the twelve study participants initially enrolled in the study.

Characteristics	Category	Resultant ± SD or percent
Age (years)	20–28 years (12)	24.33 ± 2.6
Race	White (9)	75 percent
	Brown (2)	16.7 percent
	Black (1)	8.3 percent
BMI	Eutrophic (10)	83.3 percent
	Overweight (1)	8.3 percent
	Obese (1)	8.3 percent
Marital status	Single (12)	100 percent
Profession	Student (6)	50 percent
	Other (6)	50 percent
Contraceptive method	Pill (6)	50 percent
	Vaginal ring (1)	8.3 percent
	None (5)	41.7 percent
Urinary tract infection	Occasionally (2)	16.7 percent
	No (10)	83.3 percent
Menarche age (years)	10–13 years (12)	11.67 ± 0.9
Constipation	Yes (3)	25 percent
	No (9)	75 percent
Sexual activity	Present (12)	100 percent

± SD – Mean and standard deviation; N (%) absolute number and relative frequency.

Ten participants completed using the cup for 3 months, and they used it on average for 10.1 ± 5.8 days. None stated vaginal irritation and/or urinary tract infections during use. One of the participants had an episode of urine leakage. Table 2 shows the individual results of the outcomes before and after using the vaginal cup for three menstrual cycles and their feedback in the diary.

Table 2. Results of the variables taken from the PERFECT Scheme, PFM tone, Manometry and ICIQ-VS questionnaire (n = 10).

Variables	Participant 1	Participant 2	Participant 3	Participant 4	Participant 5	Participant 6	Participant 7	Participant 8	Participant 9	Participant 10
PERFECT
Power (assessment)	4	5	4	5	5	4	3	5	5	4
Power (reassessment)	5	5	5	5	5	4	4	5	5	4
Endurance (s) (assessment)	10	10	10	10	10	6	4	10	10	10
Endurance (s) (reassessment)	10	10	10	10	10	8	6	10	10	8
Repetition (assessment)	5	10	7	10	10	6	6	10	10	7
Repetition (reassessment)	10	10	10	10	10	8	7	10	10	10
Fast (assessment)	10	10	10	10	10	10	10	10	10	10
Fast (reassessment)	10	10	10	10	10	10	10	10	10	10
Manometry
VRP (cmH2O) (assessment)	22.7	20.8	22.9	21.5	22.0	22.9	29.9	21.6	21.5	21.8
VRP (cmH2O) (reassessment)	20.2	20.6	21.0	20.4	20.4	20.3	20.3	20.3	20.0	20.1
MVC (cmH2O) (assessment)	56.8	65.8	38.6	61.7	38.5	38.2	38.8	41.6	47.1	35.7
MVC (cmH2O) (reassessment)	59.7	64.6	41.6	63.8	70.5	45.8	35.8	50.1	70.4	37.1
PFM Tone
PFM Tone (assessment)	Hypertonic	Normotonic	Hypertonic	Normotonic	Hypertonic	Hypertonic	Hypertonic	Normotonic	Hypertonic	Normotonic
PFM Tone (reassessment)	Normotonic	Normotonic	Normotonic	Normotonic	Normotonic	Normotonic	Hypertonic	Normotonic	Normotonic	Normotonic
ICIQ-VS scores
Vaginal symptoms (assessment)	6	2	12	0	6	2	12	0	7	2
Vaginal symptoms (reassessment)	4	2	6	0	2	2	10	0	2	6
Sexual matters (assessment)	10	0	28	0	8	0	20	0	0	0
Sexual matters (reassessment)	0	0	0	0	1	0	12	0	0	0
Overall impact on QOL (assessment)	4	0	6	0	2	0	4	0	2	0
Overall impact on QOL (reassessment)	0	3	2	0	1	0	3	0	1	0
Diary of menstrual cup
Discomfort while using
First cycle	+	+	−	+	+	+	−	+	+	−
Every cycle	−	−	+	−	−	−	+	−	−	+
Discomfort to remove	+	+	+	−	−	−	+	+	+	−
Episodes of vaginal irritation	−	−	−	−	−	−	−	−	−	−
Episodes of leakages	−	−	−	−	−	−	−	−	+	−
Continue to use in the future	+	+	+	+	+	+	−	+	+	+
Physical activity	Gym	Pilates	None	Gym	Walking	Swimming	None	Walking	None	Gym

VRP: vaginal resting pressure; MVC: maximal voluntary contraction; PFM: pelvic floor muscles; ICIQ-VS: International Consultation on Incontinence Questionnaire – Vaginal Symptoms; QOL: quality-of-life, +: positive; −: negative.

Regarding acceptability, seven women reported some discomfort in the first menstrual cycle while three revealed discomfort during the whole experiment.

In what relates PFM function, two participants were not able to hold the MVC for 10 s in neither the evaluations. Five of ten participants were not able to achieve ten reps it in the assessment, and in the reassessment session 2 of them still didn’t succeed.

Overall, there was an improvement in the mean values of MVC assessed by manometry, and a decrease in the VRP. There was no difference in strength, endurance or fast muscle contractions when evaluated by digital palpation. However, there was an increase in the number of repetitions of sustained muscle contractions (Table 3). Table 3 shows the effect size and power of the primary outcomes of the study.

Table 3. Assessment of the pelvic floor muscle strength of women using the PERFECT scheme, manometry, and ICIQ-VS scores before, and after three menstrual cycles using the menstrual cup (n = 10).

Variable	Assessment Median (IQI: 25–75)	Reassessment Median (IQI: 25–75)	p-Value	Effect Size	Power
PERFECT
Power	4.5 (4–5)	5 (4–5)	0.083	0.5	0.41
Endurance (s)	10 (9–10)	10 (8–10)	0.564	0.0	0.05
Repetition	8.5 (6–10)	10 (9.5–10)	0.042*	0.67	0.59
Fast	10 (10–10)	10 (10–10)	0	—	—
Manometry
VRP (cmH2O)	21.9 (21.5–22.9)	20.3 (20.1–20.4)	0.005*	1.77	0.99
MVC (cmH2O)	40.2 (38.4–58.0)	54.8 (40.5–66.0)	0.032*	0.64	0.57
ICIQ-VS (scores)
Vaginal symptoms	4 (1.5–8.25)	2 (1.5–6.0)	0.140	—	—
Sexual matters	0 (0–12.5)	0 (0–0.25)	0.068	—	—
Quality of life	1 (0–4)	0.5 (0–2.25)	0.167	—	—

Endurance (duration of sustained muscle contraction); Fast (number of rapid contraction repetitions); IQI, interquartile interval; Power (strength); Repetitions (number of sustained muscle contraction repetitions).

Analyzing individually, the values of VRP during reassessment were lower than that of the initial assessment for all women, while the value of the MVC increased for eight of the ten participants. Among these eight women, six were initially classified as having hypertonic PFM, and in the follow-up evaluation five of them evidenced normal muscle tone. The four women initially classified as having normotonic PFM showed lower values for VRP and higher values for MVC than those with hypertonic PFM in the assessment (21.5 ± 0.43 cmH₂0 vs. 22.8 ± 0.42 cmH₂0, and 51.6 ± 14.8 cmH₂0 vs. 38.5 ± 9.2, VRP and MVC, respectively).

Regarding secondary outcomes in the individual ICIQ-VS scores, only participants 4 and 8 revealed having no complaints at all regarding vaginal symptoms nor negative impact in their sexual activity or their QOL, either in the assessment and follow-up, despite the discomfort felt when using and removing the menstrual cup in the first cycle. Women with higher scores in those three domains in the assessment were the ones classified as having hypertonic PFM.

Discussion

This case series demonstrates four main findings after a period of three menstrual cycles using the menstrual cup: (1) women with higher scores of vaginal symptoms are those with PFM hypertonicity and higher values of VRP, (2) the use of menstrual cup was associated with a decrease in the VRP and an increase in the values of MVC assessed by manometry; (3) there was an increase in the number of sustained repetitions of muscle contraction, and (4) using the menstrual cup lead to changes in PFM tone.

Regarding the acceptability of using the menstrual cup, all women reported it as a positive experience, with only one mentioning an episode of menstrual fluid leakage. Two participants abandoned the study due to difficulties in adapting, similarly to what was previously described by Stewart, Greer, and Powell (2010). Moreover, seven of ten women described discomfort only in the first cycle, which is in line with other studies, where usually discomfort was reported during the first 12 days of use (Howard et al. 2011; Hyttel et al. 2017; Oster and Thornton 2012).

To the authors’ best knowledge, this is the first case series that has assessed the use of menstrual cup in the PFM variables. Our series of patients illustrate this combination of findings. Our hypothesis was that the MC device could provide a stretch stimulus by putting constant pressure on the vagina walls, and promote PFM relaxation in long term. We found that women with PFM hypertonicity were the ones with higher values of VRP and exhibited lower values of MVC. Vaginal pressure profiles may be seen as representative of the strength of PFM muscles (Shishido et al. 2008), and evaluating the VRP is one of the variables when evaluating their hypertonicity (Butrick 2009). So, physiologically, as muscles increase their tone, the ability to perform MVC decreases (Faubion, Shuster, and Bharucha 2012), which could explain the results. On the other hand, the basal differences in the values of VRP and MVC among the ten participants may be due to variations in anatomic and muscle condition. To further contribute to this variance, women with hypertonic PFM can show inconsistent baseline between contractions (Bø et al. 2017). Among the five women who couldn´t perform the ten MVC repetitions with a rest period, four were classified as having hypertonic PFM, and this slow de-recruitment can be indicative of hypertonicity (Bø et al. 2017). Even though two participants were not able to accomplish performing the ten reps in the reassessment, both improved their scores, which may be indicative of a better transition between the two states. However, further studies are necessary to confirm one of the hypotheses.

Another perceived PFM function was the significant increase in the number of repetitions through the PERFECT scheme. According to Bø et al. (2017), this condition involves PFM endurance, considering the ability to repeatedly develop MVC. This aspect ends up involving the parameters described above, as well as being related to the instructions given by the manufacturer to perform PFM contractions for the use of the menstrual cup.

A study from Naess and Bø (2018) showed significant decrease in VRP when women were taught to correctly perform three MVC, suggesting that MVC may be a method of reducing PFM hypertonicity. Our participants evidenced a decrease in VRP and an improvement in MVC. Women were instructed to perform PFM contraction to ensure appropriate placement of the menstrual cup, and this can be the effect that we have registered. However, no data were recorded regarding PFM contraction during the use of the menstrual cup. On the other hand, it is known that the PFM have adaptive capacity through time, and when there is a load or resistance applied, it can lead to local changes (Bø, Talseth, and Holme 1999; Oblasser, Christie, and McCourt 2015). So, as VRP had a significant reduction, we suspect that the menstrual cup was acting similarly to a vaginal dilator, by regaining elasticity in the PFM and vaginal walls and helping to reduce muscle tightness and vaginal soreness (Cullen et al. 2012; van Reijn-Baggen et al. 2022). However, there is a need for a randomized controlled trial of high methodological quality to explore this question.

Vaginal symptoms were present in women with hypertonic muscles (mostly pain, tightness, and reduced lubrication) (Reissing et al. 2005), and two of three women who reported discomfort in all the cycles where the ones with higher scores in the sexual domain of the ICIQ-VS questionnaire. From the six women initially reported as having hypertonic muscles, five were evaluated as normotonic after using the menstrual cup. Agreeing with this, the ICIQ-VS questionnaire evidenced an overall reduction in vaginal symptoms after the 3 months of use.

This study has limitations that must be addressed. It is the first study evaluating the influence of the menstrual cup in the PFM, and therefore literature is scarce to discuss our findings. Furthermore, the small sample size and the short period of use are additional restraints. Therefore, additional studies evaluating PFM tone and strength for a period longer than three menstrual cycles are of great interest to substantiate and confirm the influence that the menstrual collector may on the PFM in the long term. Certainly, further research is indicated to repeat this study using a randomized-controlled clinical trial design with long-term follow-up and greater subject numbers.

Conclusions

In conclusion, this study provides preliminary case-based evidence that the use of the vaginal cup for a period of three menstrual cycles changed the PFM tone and VRP, as well as improve the MVC, and repetitions of PFM assessed by digital palpation. Moreover, the women reported the use of vaginal cup as a positive experience.

Acknowledgments

The authors truly acknowledge the women who participated in this study and to Conselho Nacional de Desenvolvimento Científico e Técnológico (CNPq) for granting project financing MCTIC/CNPq nº28/2018 Process 425029/2018-2.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the Conselho Nacional de Desenvolvimento Científico e Técnológico (CNPq) - MCTIC/CNPq nº28/2018 under Grant [425029/2018-2].