Urologists at Aarhus University Hospital in Denmark have found that improper placement of a menstrual cup can cause ureterohydronephrosis, an abnormal enlargement of the kidney and ureter associated with impaired urine outflow. The case is described in a research paper in the journal BMJ Case Reports. According to the researchers, this condition can lead to kidney cell death and subsequently to acute renal failure. Such cases are extremely rare in the scientific literature - only five such episodes have been reported so far. In the new study, scientists analyzed the health of a 30-year-old woman who went to the doctor with complaints of blood in the urine and pain in the right side and lower abdomen, which bothered her for about six months. The patient's medical history noted the removal of a kidney stone. The woman also disclosed that she used the menstrual bowl on a regular basis. A menstrual cup is a device made of medical-grade silicone that is inserted into the vagina in a compressed state and used to collect blood. In recent years, this personal hygiene product has gained popularity due to its durability and environmental friendliness. A CT scan showed enlargement of the right kidney and ureter, and misplacement of the cup near the mouth of the ureter in the vagina. After recommending discontinuation of the bowl and a follow-up examination one month later, the symptoms disappeared. This confirmed that the misplaced bowl was interfering with normal urine outflow. The study authors urged doctors and patients to be more aware of the possible risks of using such a hygiene product. “Correct positioning, as well as choosing the appropriate shape and size of the bowl, are important to prevent negative effects on the upper urinary tract,” the researchers explained.