Several women have blamed menstrual cups for triggering their pelvic organ prolapse.
The feminine hygiene product sits in the vagina, collecting blood during menstruation.
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An alternative to sanitary towels and tampons, the reusable cups are sold as being more affordable, environmentally friendly and absorbent.
Many claim they are safer than tampons due to a reported lower risk of the rare, but life-threatening, condition toxic shock syndrome (TSS).
Several women have since told the BBC’s flagship Victoria Derbyshire show they developed pelvic prolapse within months of switching to a menstrual cup.
Menstrual cups are classed as a medical device and are therefore not subject to the same stringent regulations as medication in the UK.
When it comes to removing the cups, physiotherapist Kate Lough told the BBC women may be “using [their] pelvic floor muscles to bring the cup lower in the vagina”.
“‘Bearing down’ on the cup to push it within reach of your fingers is not good pelvic floor advice,” she said.
“It counters the advice women would be given to avoid prolapse.”
Pelvic floor exercises can ward off vaginal prolapse.
One who knows the dangers of incorrect menstrual cup use all too well is Jenny, who developed minor pelvic organ prolapse three months into switching to the feminine hygiene product.
This occurs when an organ in the pelvis slips from its normal position and bulges into the vagina.
Although not serious, many patients endure a “dragging discomfort” in their vagina, as well as heaviness in their lower abdomen and discomfort during sex.
Jenny claims she read the cup’s instructions thoroughly, with there being no mention of prolapse as a possible side effect.
Another patient, who chose to go by Maria, started using a menstrual cup two months ago.
Maria was a “convert” until she developed minor vaginal prolapse.
A gynaecologist reportedly told her “that probably happened because of the cup”.
Research suggests, however, menstrual cups are safe for the most part.
Last year, scientists from the Liverpool School of Tropical Medicine analysed the “leakage, acceptability, safety and availability” of the cups across 43 global studies with more than 3,300 participants.
Just five women reported “severe pain or vaginal wounds”, The Lancet Public Health journal reported.
Six developed “allergies or rash” from using the cups, which are typically made of rubber or silicone.
Nine women had “urinary tract complaints” and five TSS.
TSS comes about when bacteria that live harmlessly on the skin enter the body and release dangerous chemicals.
Using tampons, particularly if they are “super absorbent” or left in for longer than the recommended four-to-eight hours, is a recognised risk.
Also linked to childbirth and cuts to the skin, CNN reported TSS affects fewer than one in 100,000 people in the US.
Many menstrual-cup manufacturers claim they can be left in for up to 12 hours, depending on the heaviness of a woman’s flow.
Although the Liverpool scientists claimed further studies are required, they concluded “menstrual cups are a safe option for menstruation management”.
Nevertheless, the Chartered Society of Physiotherapy is calling for the cups to be better regulated, with more informed safety advice on the label.
How to insert and remove a menstrual cup
Like with tampons, women should wash their hands before inserting or removing a menstrual cup.
When it comes to insertion, the cup should be folded so it can enter the vagina, said Lough.
Once inside, release the hold so the cup opens “like a pop-up tent”.
The suction effect should enable the cup to sit in the vagina, collecting menstrual blood.
To remove the cup, Lough recommends squeezing the bottom of the device to release the suction effect.
Alternatively, women can place their finger higher in the vagina and release the suction in the rim at the top of the cup.