HIV remains a global pandemic with 37 million infected. In western Kenya, 16% of women in the general population and 29% of the poorest women have HIV. The HIV and sexually transmitted infection (STI) epidemics overlap with broader reproductive health concerns. Menstrual hygiene management is a big problem in low- and middle-income countries and a lack of menstrual products negatively impacts women's work-life. This comes from cultural taboos, stigma, and discrimination, promoting secrecy around menstruation, high cost of menstrual products, use of traditional materials (e.g. rags, cotton wool, etc.) causing leakage and odor, and lack of water and safe hygiene facilities. Menstrual cups designed for use during sex may help women prevent Bacterial vaginosis (BV) and STIs through hygienic period practices, and may help them avoid bad practices in an attempt to maintain vaginal dryness. The goal of this interventional trial is to test the impact of menstrual cups on vaginal microbiome, BV, and STIs of poor women at high risk for STIs and HIV. We predict to see 25% less BV, our primary outcome, over one year. This trial aims to learn more about the safety of the intervention, and understand what is needed to fully implement the program.