To compare the effects of fresh embryo transfers (ET) and elective frozen-thawed embryo transfer cycles in poor ovarian responders.

Inclusion Criteria:

• All patients that fulfill the Bologna criteria [at least 2 of the following 3 features must be present: (i) advanced maternal age or any other risk factor for POR; (ii) a previous POR; and (iii) an abnormal ovarian reserve test (ORT)]
• if the progesterone serum level was ≤1.5 ng/mL on the trigger day.
• body mass index 18-32 kg/m2
• Both partners are able to provide written informed consent.
• At least 1 good quality embryo on day 3 after egg collection on day 3 according to the Istanbul consensus (7-8 cells; with symmetric blastomeres and <10% fragmentation by volume).
• Endometrial thickness ≥8 mm on trigger day.
• a normal uterine cavity on ultrasound.
• IVF/ICSI with only fresh semen

Exclusion Criteria:

• Pre-implantation genetic testing is being planned.
• if they had severe endometriosis, uterine pathology (myomas, adenomyosis, endocrinopathies, adhesions, acquired or congenital abnormalities), untreated tubal hydrosalpinges, ovarian tumor, recurrent spontaneous abortion, implantation failure after ≥ 2 fresh or frozen ET.

Blinding of the allocated intervention is not possible.