Young women with menstruation-related disorders, such as endometriosis and dysmenorrhea (painful periods), were significantly more likely to be diagnosed as having an STI than women without those conditions, according to a large study from Japan published this week in PLOS One.
Endometriosis occurs when tissue similar to uterine tissue grows outside the uterus. While not strictly a menstrual disorder, it can cause pain, irregular periods, and infertility.
For the study, researchers led by a team at University of Yamanashi in Japan and funded by Rohto Pharmaceutical Co. examined health insurance claims data for more than 3.4 million women ages 40 and under who had at least one healthcare visit in 2023.
They found that roughly 260,000 women (7.5%) had been diagnosed as having endometriosis, dysmenorrhea, or both, and that those women were four to five times more likely to be diagnosed with an STI.
Women with endometriosis have highest STI rates
Across all STI categories the researchers examined—gonorrhea, chlamydia, trichomoniasis, genital herpes, and other STIs—diagnoses were significantly more common among women with menstrual disorders.
Chlamydia was identified in 3.5% of women with menstrual disorders, compared with 0.7% of women without, representing a fivefold increase and the largest difference in prevalence between women with and without menstrual disorders.
Similarly, gonorrhea was diagnosed in 0.9% of women with menstrual disorders, compared with 0.2% of those without, which also translates to a roughly fivefold increase. Trichomoniasis, genital herpes, and other STIs were also diagnosed between four to five times more often in women with menstrual disorders.
Women who had been diagnosed with endometriosis, dysmenorrhea, or both were four to five times more likely to be diagnosed with an STI.
Women with endometriosis had the highest STI diagnosis rates overall. Nearly 5% were diagnosed as having chlamydia, making it the most common STI in this group and representing a more than sevenfold increase compared with women without menstrual disorders. Women with dysmenorrhea also had elevated rates of every STI studied.
The study found little evidence that hormonal treatments such as low-dose estrogen-progestin therapy, affected STI risk. Differences between women who used hormonal therapy and those who did not were generally less than 1 percentage point.
More frequent healthcare visits may explain findings
The researchers suggest several hypotheses for the association between menstrual disorders and STIs.
One likely explanation is that women with endometriosis and dysmenorrhea have more frequent healthcare visits. Because many STIs produce only mild symptoms, women who seek care more often for menstrual conditions may simply be more likely to have infections detected.
The researchers also said biological and behavioral factors could play a role. Menstrual disorders, especially endometriosis, are associated with inflammation, pain during sex, and sexual dysfunction, all of which could influence contraceptive practices and susceptibility to infection. Yet the authors caution that these possible mechanisms “remain speculative.”
While the findings should be interpreted cautiously because of the differences in healthcare-seeking behavior between women with menstrual disorders and women without, they also underscore the importance of STI screening and reproductive health education for these patients, conclude the authors.
