This study intends to explore the correlation between cervical microbiome, gut microbiome and pregnancy outcomes of frozen embryo transfer patients through a multicenter prospective observational study, and to explore the predictive value of microbiome on pregnancy outcome.

Inclusion Criteria:

1. Infertile women receiving assisted reproductive technology treatment, preparing for frozen embryo transfer cycle;
2. Female age: 20-45 years old;
3. Single frozen-thawed blastocyst Transferred
4. Endometrial thickness ≥7mm on the day of luteal transformation
5. Written informed consent.

Exclusion Criteria:

1. Women who have pathologies or malformations that affect the pregnancy outcome:genital malformations, intrauterine adhesions, uterine fibroids (>4 cm in diameter or compressing endometrial line), adenomyosis, endometrial polyps; untreated tubal pleura Presence of autoimmune disease;
2. Untreated hyperprolactinemia, thyroid disease, adrenal disease
3. Antibiotic use within the past 7 days;
4. Current or recent (within 3 months) drug abuse, including alcohol and tobacco;
5. Refused or unable to comply with protocol requirements;
6. Participation in any experimental drug study within 60 days prior to screening.

Patients attending Center of Reproductive Medicine