Flo Digital Contraceptive Study

The goal of this clinical trial is to learn if the Flo Digital Contraceptive (FDC) app can effectively prevent unintended pregnancy in women aged 18 years and older residing in the United States. The main questions it aims to answer are: What is the rate of unintended pregnancy in women aged 18-35 years using FDC as their sole method of contraception under typical-use conditions, measured using the Pearl Index? What is the cumulative probability of unintended pregnancy over 13 menstrual cycles for all participants, including those with regular and irregular cycles? Participants will: Use the Flo Digital Contraceptive app in 'prevent pregnancy' mode as their primary method of contraception for up to 13 menstrual cycles or 18 months, whichever comes first Wear an Apple Watch (Series 8 or later, or Ultra) while sleeping to collect nightly wrist temperature data, which the app uses to detect ovulation Log menstrual cycles, sexual activity, and any use of emergency contraception directly in the Flo app Complete monthly electronic surveys (ePROs) administered by the study team covering pregnancy status, adherence, safety, and experience Complete a baseline demographic survey at enrollment and an exit survey at the end of participation

Inclusion Criteria: * Adults with female reproductive organs aged ≥18 years * Reside in the United States of America * Have menstrual frequency (i.e., interval between first day of bleeding each cycle) between 16-90 days * Sexually active, having vaginal sex with male partner(s) without known fertility problems AND where neither partner has a known, or is at high risk of, sexually transmitted infections (STIs). * Desiring contraception, i.e., planning to prevent pregnancy and not currently trying or planning to conceive for at least 12 months, and up to 18 months. from enrollment * Willing and able to use FDC as advised, including ability to: * (1) Abstain from penile-vaginal intercourse on days indicated as "Use protection" OR * (2) Use barrier methods (such as condoms) for penile-vaginal intercourse on days indicated as "Use protection" * Possession of an iOS mobile device (version 16 or higher) with internet connectivity * Sufficient English language proficiency and knowledge of English language required for correct use of the intervention and mobile device * Willing to wear a functional Apple Watch capable of sensing wrist-skin temperature (Series 8 or later, Ultra) while sleeping, with it connected and sharing temperature data to the Flo application * No known pregnancy at the time of enrollment * Willing and able to provide valid consent Exclusion Criteria: * Current use of any contraceptive medication, implant or technique, including but not limited to: * Oral contraceptive pills * Hormonal implants, injections, vaginal rings or transdermal patches * Intrauterine devices (copper and/or levonorgestrel) * Surgical sterilization (tubal ligation, salpingectomy, intrafallopian tube coils) * ≤12 weeks postpartum (second or third trimester pregnancy)\* * \*Includes terminations of any pregnancy \>14 weeks OR have given birth \>12 weeks postpartum without return of at least one menses * Postabortion (first trimester miscarriage, ectopic, termination) who have: * History of cycles outside the 21-35 day range, OR * Not had return of at least one menses following the abortion * Currently lactating (breastfeeding, pumping or otherwise), regardless of interval since last pregnancy * Had fewer than 9 menstrual cycles in the past 12 months * Have received medical advice from a healthcare provider that pregnancy is medically contraindicated, irrespective of whether this is due to a medical condition or risk, or due to medication being taken, or other reason. * Participants must be willing to NOT use condoms for penile-vaginal intercourse. Those who are unable or unwilling to restrict use of condoms for penile-vaginal intercourse for any reason, including but not limited to compromising health and/or safety of self or others will be excluded * Note: Use of barrier contraceptive for sexual encounters that could not result in pregnancy, such as oral or anal sex, is not restricted * Any condition or circumstance that, in the opinion of the Lead Investigator (LI) or designee, would compromise the participant's ability to comply with the study protocol, pose an unacceptable risk to the participant's safety or well-being, or interfere with the evaluation of study objectives * Concurrent participation in another research study that aims to prevent pregnancy * Extreme shift work patterns (e.g., unpredictable or rotating shifts changing more frequently than weekly, frequent time zone changes) that prevent consistent sleep schedules necessary for reliable temperature measurement