The main objective of this study is to compare clinical pregnancy rates between two groups of women who have progesterone levels below 10 ng/mL on the day of frozen embryo transfer: group 1 (vaginal micronized progesterone supplemented with progesterone intramuscular 50 mg per day) and group 2 (vaginal micronized progesterone with no supplementation)

Trial Design:

Single center, longitudinal, randomized, interventional, controlled, pharmacological study, enrolling women attending clinical Centers of medically assisted reproduction (ART).

The study protocol consists in the record of all the diagnostic and clinical outcome parameters, according to clinical practice, for the following patient cohorts:

• The patients who are undergoing frozen embryo transfers with blastocyst or cleavage stage embryos and have progesterone levels below 10 ng/mL on the day of embryo transfer

• Study groups

  • Group supplemented with progesterone intramuscular 50 mg per day until the day of beta-hcg testing (Intervention group);

  • Group with no supplementation (Control group).

    • Endometrial cycle is started with estradiol valerate dose of 4 mg to 8 mg per day, the patients then are appointed to have ultrasound scan of their endometrium every 3 to 7 days and the dose of estradiol may be increased to 16 mg per day maximum depends on the thickness of endometrium; when their endometrium reach 8 mm or higher and duration of endometrial preparation is ≥ 12 days, the embryo transfer will be planned and transvaginal progesterone are prescribed according to the day of transfer.
    • If this is the first cycle of embryo transfer and she is < 35 years of age, 1 grade 1 embryo is transferred, otherwise 2 embryos are transferred.
    • In the morning of embryo-transferred day, all patients will have their blood tested for progesterone levels, if their levels below 10 ng/mL, they will be recruited into the study and randomized into two groups.
    • In the study group, the patients will be prescribed with intramuscular progesterone supplemetation 50 mg + 800mg vaginal micronized progesterone per day for 14 days, until the day of beta-hcg testing.
    • In the control group, the patients will continue their regular medications (800mg vaginal micronized progesterone per day) until the day of beta-hcg testing without any progesterone supplementation.
    • If the beta-hcg test is positive, the patients will be continued their prescriptions depending on study or control group as mentioned above till 7 weeks of pregnancy when the fetal heart can be confirmed, then the patients will be followed up till 11 - 12 weeks of pregnancy

Inclusion Criteria:

• Patients undergone ART with frozen embryo transfer, blastocyst or cleavaged stage embryo transfer, from 18-45 years of age
• Normal BMI
• HRT for Endometrial preparation in FET cycles

Exclusion Criteria:

• Oocyte donor cycles
• Surrogacy
• IVM
• PGT
• Abnormal Uterine (firbroids 0 -> 3 according to FIGO classification, polyp, adenomyosis, congenital malformation)
• Uterus fibroids type 4,5 (Figo classification) > 4cm
• History of recurrent implantation failure
• Endometrial thickness <7mm on the day of ET
• Cesarean scar defect (isthmocele)

We want to investigate on the pregnancy outcome, therefore only female patients will be recruited