Effect of FB301 on Vaginal Bacterial Profile in Women With Asymptomatic Vaginal Dysbiosis Undergoing a Mock Frozen Embryo Transfer Cycle

Inclusion Criteria

• Able to understand the study and sign a consent form.
• Is a woman aged 18 to 45 years.
• Still has regular menstrual periods (pre-menopausal).
• Has had at least one previous frozen embryo transfer (FET) that did not result in pregnancy within the past 3 years, and this was not due to either male infertility or blocked /damaged fallopian tubes.
• Willing to take part in mock frozen embryo transfer (FET) cycle and is considered medically suitable to subsequently have a frozen embryo transfer (FET) using one good-quality embryo (grade 3BB or higher).
• Willing to have only one embryo transferred during the study cycle.
• A vaginal swab taken at the first study visit shows a specific vaginal microbiome imbalance required for this study (vaginal molecular dysbiosis).
• An ultrasound scan shows no problems with uterus or pelvis that would prevent pregnancy or greatly reduce the chance of pregnancy.
• Recent fertility blood tests show FSH less than 12 IU/L (within the last 6 months)
• Recent fertility blood tests show AMH greater than 1 ng/mL (at the time of oocyte retrieval).
• Body mass index (BMI) is between 18 and 42 kg/m².
• From the first study treatment until the mock FET cycle, agrees to:

• Avoid vaginal intercourse or use condoms (without spermicide or lubricant),
• Avoid swimming or hot tubs,
• Avoid using tampons, menstrual cups, sex toys, vaginal cleansers, lubricants, or other vaginal products unless approved by the study team.
• Willing to answer questions about sexual and reproductive activity during the study.
• Willing to provide vaginal swab samples at the clinic.
• Willing to receive the first study treatment in the clinic and use the study treatment at home as instructed.
• Screening blood tests are negative for hepatitis B, hepatitis C, HIV, and syphilis.
• Willing to attend all study visits and follow-up assessments and provide information about pregnancy and newborn health outcomes.

Exclusion Criteria

• History of five or more failed frozen embryo transfers (FET) in the past 5 years.
• Have a condition that weakens the immune system (such as uncontrolled diabetes, active cancer, or an organ transplant).
• Currently taking medications that suppress the immune system (such as systemic steroids, biologics, chemotherapy, or transplant medications).
• Is already pregnant before completing the mock FET cycle.
• Test positive for a sexually transmitted infection (such as chlamydia, gonorrhea, Mycoplasma genitalium, or Trichomonas vaginalis).
• Current vaginal yeast infection that requires treatment.
• Cannot safely take the hormone medications required for a frozen embryo transfer (such as estradiol or progesterone).
• Use of intravaginal progesterone gels or solutions.
• Needs regular antibiotics or are likely to require antibiotics during the study.
• Has taken oral, injectable, or vaginal antibiotics within 30 days before screening.
• History of gynecological cancer or other significant gynecological condition that would make participation unsafe.
• Has a medical condition that would make participation unsafe or difficult.
• Has an unstable medical or psychiatric condition that could make it difficult to follow study requirements.
• Has any other condition that could interfere with participation.