Biomarkers of Endometrial Receptivity

Inclusion Criteria - Arm A - stimulated cycle: * female aged less than 37 years (maximally 36y + 364d) * no smoker * normal menstrual cycles lasting between 25 to 35 days * had been infertile for less than five years * normal responder * fewer than three failed cycles of assisted reproduction treatment, including fresh IVF/ intracytoplasmic sperm injection (ICSI) embryo transfer cycles and/or frozen-thawed embryo transfer cycles * sperm obtained through ejaculation * spermiogram more than 5 million sperm/mL * BMI 19-29 kg/m2 * follicle stimulating hormone (FSH) \< 10 IU/L on the third day * basal antral follicle count of 5-15 * undergoing the same routine gonadotrophin-releasing hormone agonist (GnRHa) long depot or gonadotrophin-releasing hormone antagonist (GnRH-ant.) protocol * informed consent Exclusion Criteria - Arm A - stimulated cycle: * genetic disease * metabolic and/or endocrine disorders * polycystic ovary syndrome (defined by the Rotterdam criteria) * women with prior diagnosis of endometriosis or adenomyosis * previous gynecological/pelvic surgery except for salpingectomy * repeated spontaneous abortions (two or more) * previously less than 5 oocytes and/or serum anti-Mullerian hormone value \< 1.0 mIU/ml or more than 20 oocytes, milli-International unit (mIU) * previous ovarian hyperstimulation syndrome (OHSS) * presence of any structural abnormality of the reproductive system * donor oocyte cycles * severe male factor infertility \< 5 million sperm/mL * low…