The aim of the present study is to determine if implantation rate could be increased in women undergoing frozen embryo transfer cycles in case of adjusting their embryo development at hatching stage.

Inclusion Criteria:

1. Patients who will agree to participate and assign an informed consent form
2. Only blastocyst transfer FET cycles
3. Patients undergoing FET after their 1st IVF or ICSI cycle with no pregnancy at the fresh transfer
4. Freeze-all cycles due to OHSS
5. Freeze-all cycles due to poor endometrium
6. Age 19-33 at the time of randomization.
7. Their frozen blastocysts are 3 or less grade of expansion.
8. Female with a ≥12 AFCs
9. Endometrial thickness ≥ 8mm at the time of ovulation
10. Women with their male partners will give only fresh semen
11. Women who have no uterine abnormality by ultrasound
12. BMI ≤ 31

Exclusion Criteria:

1. Cycles undergoing preimplantation genetic diagnosis.
2. Women who have previous two cycles of implantation failure at fresh transfer
3. Women who have previous two FET failed cycles
4. Any uterine pathology (myomas, adenomyosis, endocrinopathies, thrombophilia, chronic pathologies, acquired or congenital uterine abnormalities)
5. Patients with severe endometriosis
6. Presence of uni- or bilateral hydrosalpinx
7. Recurrent pregnancy loss.
8. Any medical condition that affect fertility.

The gynecologist performing the embryo transfer as well as the patients undergoing frozen embryo transfer will be blinded to group allocation