Effectiveness of the Natural Cycles birth control app

A Prospective Observational Study on the Contraceptive Effectiveness of the Natural Cycles Application (The VENUS Study)

This study will test how well the Natural Cycles app prevents pregnancy over one year in sexually active women aged 18 to 35 with no known infertility.

Quick facts

• Study type: Observational
• Enrollment: 2000 (estimated)
• Ages: 18 Years to 35 Years
• Sex: Female
• Sponsor: Natural Cycles (Industry-sponsored)
• Drugs / interventions: Methotrexate
• Locations: 1 site (New York, New York)
• Trial ID: NCT07566793 on ClinicalTrials.gov

What this trial studies

This is a prospective, single-arm observational study in which participants use the Natural Cycles app for up to 13 cycles while logging daily sexual activity and menstrual/temperature data. Participants will perform urine pregnancy tests provided by mail at study entry, at the start of each cycle, and at exit, and will complete questionnaires at enrollment and study end. The study will calculate both typical-use pregnancy rates for all users and perfect-use pregnancy rates for users who follow the app's instructions exactly, using cycle-by-cycle data to meet regulatory standards. The design aims to overcome limitations of passive data collection by systematically capturing intercourse and pregnancy outcomes.

Who should consider this trial

Good fit: Ideal participants are sexually active women aged 18–35 who want to avoid pregnancy for 13 cycles, have cycle lengths of about 21–35 days, are willing to rely solely on Natural Cycles and to log daily data and perform mailed pregnancy tests, and who have no known infertility or permanent/hormonal contraception.

Not a fit: People unlikely to benefit include those who prefer or require hormonal or permanent contraception, those outside the age or cycle-length criteria, individuals unwilling to log daily data or do mailed tests, and EU citizens who are excluded.

Why it matters

Potential benefit: If successful, this will give clearer, regulatory-grade information about how well Natural Cycles prevents pregnancy in real-world and perfect-use conditions.

How similar studies have performed: Previous large observational analyses of Natural Cycles have demonstrated contraceptive effectiveness, but this prospective, cycle-by-cycle approach is a more rigorous design intended to meet evolving regulatory expectations.

Eligibility criteria

Inclusion Criteria:

* Wants to avoid pregnancy for 13 cycles.
* Is willing to rely solely on Natural Cycles as their sole contraception method for 13 cycles.
* Is not currently using permanent contraceptive methods, such as sterilization (of either the user or their partner), or hormonal methods, such as the hormonal contraceptive implant or IUD.
* Has an intact uterus, both ovaries and both fallopian tubes to the best of their knowledge.
* Has an average cycle length between 21 and 35 days. The user anticipates heterosexual intercourse at least once a month in the next year.
* Is willing to enter data on a daily basis and perform pregnancy tests as requested by protocol.
* Is willing to complete a satisfaction survey at the end of her study participation.

Exclusion Criteria:

* Has EU-citizenship
* Has had a Depo-Provera injection in the last 10 months or has had less than three consecutive, spontaneous menstrual cycles since their last injection.
* Has had less than three consecutive, spontaneous menstrual cycles after removing a hormonal implant.
* Has had less than three consecutive, spontaneous menstrual cycles after the end of a pregnancy.
* Has had less than three consecutive, spontaneous menstrual cycles since she last breastfed.
* Has (or partner has) known fertility issues, such as infertility and sterilization, or have been advised by a healthcare professional that they may have difficulty conceiving for any reason.
* Has a medical condition possibly impacting fertility, i.e. endometriosis, a history of Pelvic Inflammatory Disease (PID), significant uterine fibroids or adenomyosis, or another diagnosed medical condition that they have been told affects fertility.
* Is regularly taking one of the following prescribed pharmaceutical medications known to be teratogenic (i.e., a medication that can cause birth defects):

Isotretinoin (like Accutane, Absorica, Claravis, or Myorisan) for severe acne Valproic acid or divalproex sodium (like Depakote, Depakene, or Topamax) for seizures (epilepsy), migraines, or bipolar disorder Methotrexate (Trexall, Rheumatrex) or leflunomide (Arava) for autoimmune conditions ACE Inhibitors (like Lisinopril, Enalapril) or Angiotensin II Receptor Blockers (ARBs) (like Losartan, Valsartan) for high blood pressure or heart conditions Warfarin (Coumadin, Jantoven) for blood clot prevention

Where this trial is running

New York, New York

• Natural Cycles USA Corp — New York, New York, United States (Recruiting)

Study contacts

• Principal investigator: Eleonora Benhar, PhD — Natural Cycles Nordic AB
• Study coordinator: Agathe van Lamsweerde, MSc

Conditions Contraception