What is the Optimal Cycle Regimen for Frozen- Thawed Embryo Transfer Cycles

What is the Optimal Cycle Regimen for Frozen- Thawed Embryo Transfer Cycles: Spontaneous Natural Cycles Versus Hormonal Replacement Treatment (HRT) Cycles

Investigators will be comparing artificial (HRT) frozen-thawed embryo transfer cycles to correctly conducted spontaneous natural cycles after the transfer of a chromosomally normal embryo.

The most common treatment protocols for frozen embryo transfers include natural cycles with or without human chorionic gonadotrophin (HCG) trigger or endometrial preparation with hormonal treatment (artificial cycles), with or without Gonadotrophin - releasing hormone agonist suppression. Recent studies comparing artificial and natural cycles concluded that the optimal means of endometrial preparation for frozen- thawed cycle remains unclear and both options may be offered to women with regular ovulatory cycles.

Correctly identified spontaneous natural cycles are the preferred option for frozen-thawed embryo transfer in women with regular menstrual cycles.

Investigators will be comparing artificial (HRT) frozen-thawed embryo transfer cycles to correctly conducted spontaneous natural cycles after the transfer of a chromosomally normal embryo.

Inclusion criteria include the following:

1. Women aged 18 years to 42 years with regular menses (26-34 days)
2. Having 1 or 2 chromosomally normal cryopreserved blastocysts available for transfer.
3. First frozen-thawed transfer cycle
4. Progesterone level < 1.5 ng/mL day of trigger injection in stimulation cycle from which embryos to be transferred were created.

Exclusion criteria include the following:

1. Polycystic ovarian syndrome
2. Poor ovarian responder in accordance with Bologna criteria
3. Uterine abnormality US / saline infusion sonohysterogram
4. Previous dilatation & curettage (D&C)
5. Hydrosalpinx
6. Asherman syndrome
7. History of endometriosis
8. ICSI due to severe male factor with testicular sperm
9. Any known contraindications or allergy to oral estradiol or progesterone.
10. Discontinuation of HRT medication ( medication error in research HRT cycle )
11. Failure to detect ovulation in the research natural cycle
12. Duration of estradiol exposure ≥ 17 days and endometrium < 6mm
13. Spontaneous ovulation in HRT artificial cycle