Single arm interventional study looking at biological outcomes at 4 time points throughout the cycle before and after taking an oral gonadotropin-releasing hormone antagonist (gnRH). Samples of whole blood, endocervical mucus, endocervical biopsy, and vaginal swab will be collected.

This study will enroll participants and obtain biological samples at 4 time points. The study will begin on the first day of menstruation following enrollment. Patients will monitor for peri-ovulation using an ovulation test that monitors for urinary metabolites for luteinizing hormone (LH). At the midluteal time point for sampling (days 6-9 after "high fertility" on ovulation test) subjects will begin taking an oral gonadotropin-releasing hormone antagonist (gnRH) (relugolix) for 10 days. Samples of whole blood, endocervical mucus, endocervical biopsy, and vaginal swab will be collected during the early follicular phase (3-5 days following the start of menstruation), peri-ovulation (9-14 days following the start of menstruation based on estriol glucuronide (E3G) urinary metabolite), mid-luteal (6-9 days following mid-cycle draw), and upon stoppage of relugolix (9-11 days following relugolix initiation).

Inclusion Criteria:

• Normal menstrual cycles of 25-35 days in length for at least the previous 3 cycles
• BMI >18 and <35
• Serum p4 >= 3 ng/ml on single sample collected between days 18-25 of self-reported menstrual cycle
• Flexible schedule allowing blood draws on less than 48 hour notice
• In good general health
• Commit to using non-hormonal contraceptive methods without spermicide during study period except those prescribed in the experimental protocol
• No objections to taking study drugs
• No objections to refraining from intercourse the night before any sampling and willing to use condoms during vaginal intercourse

Exclusion Criteria:

• Oral contraceptive use or other hormone supplement within the preceding 2 months
• Current cervical infection
• Evidence of abnormal cervical cytology
• Use of any IUD for contraception
• Long-acting hormonal contraceptive use in the past 12 months (e.g., Depo-Provera)
• Contraindications to study drugs
• Current or past pregnancy within the previous 6 months or currently trying to conceive
• Desiring to conceive in the next 8 months
• Breastfeeding in the past 2 months
• Diagnosed diabetes or metabolic syndrome
• Diagnosed Polycystic Ovary Syndrome
• History of, or self-reported, substance abuse
• Smoker
• Previous infertility treatment excluding male factor issues
• Use of an investigational drug within the past 2 months
• History of excisional or ablative treatment procedure on cervix (i.e., LEEP, Cryotherapy, Cold Knife Cone)
• Current treatment for a vaginal infection such as bacterial vaginosis
• History of venous thromboembolism (VTE) or inherited thrombophilias