IUD showdown: which type keeps vaginal bacteria healthier?

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: * Willing and able to provide written informed consent for screening and trial participation * Desire and willingness to use either IUD or IUS for contraception for at least one year * Clear understanding of study randomization and commitment to use the assigned IUD * Between 18 and 40 years of age (inclusive) * Willing and able to actively participate in the study for 12 months * Willing to be tested for HIV * Sexually active * HIV-negative * Would benefit from STI prevention Exclusion Criteria: * Living with HIV or HIV screening results that are not definitively negative * Currently pregnant or planning to become pregnant within the next 12 months * Documented or known history of infertility or sterilization * Prior history of ectopic pregnancy * Use of contraceptive implant, IUD or injectable progestin in the past 3 months * Use of oral contraceptives in the past 30 days * Planning to use alternative contraception except condoms for the trial duration * 0-6 weeks postpartum * Has had a hysterectomy or sterilization * History of challenges using and IUD/IUS, including frequent expulsion * Medical contraindications (Category 3 or 4 criteria as detailed in the WHO MEC1 to copper IUDs or LNG-IUS, including: * Endometrial, ovarian, or cervical cancer * Unexplained vaginal bleeding between menstrual periods or bleeding after intercourse * History of pelvic tuberculosis * Anatomical abnormality of the uterus incompatible with IUD insertion * A recent septic abortion * Untreated mucopurulent cervicitis on exam, untreated pelvic inflammatory disease (PID), or untreated known gonorrhoea or chlamydia * Has any condition (social or medical), which in the opinion of the investigator, would make study participation unsafe or complicate data interpretation