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 response to stimulation

• endometrium < 8 mm at the day of human chorionic gonadotropin (hCG) or ET

• number of retrieved oocytes 5 - 20

• low fertilization capacity (rate of fertilization < 20% and late ICSI following IVF fertilization failure)

• OHSS

• IVF cycle cancelled before ET

• other than easy one high-quality blastocyst transfer (at least grade 3BB)

Inclusion criteria - Arm B - substituted 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 at stimulation

• 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

• FSH < 10 IU/L on the third day

• undergoing the same routine estrogen/progesterone substituted cycle

• informed consent

Exclusion criteria - Arm B - substituted cycle:

• genetic disease

• metabolic and/or endocrine disorders such as diabetes, metabolic syndrome, and thyroid disorders

• polycystic ovary syndrome (defined by the Rotterdam criteria), hyperprolactinaemia

• 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 < 0.5 mIU/ml in the stimulated cycle

• previous OHSS

• presence of any structural abnormality of the reproductive system

• severe male factor infertility < 5 million sperm/mL in the stimulated cycle

• number of retrieved oocytes 5 - 20 in the stimulated cycle

• low fertilization capacity (rate of fertilization < 20% and late ICSI following IVF fertilization failure)

• endometrium less than 8 mm at the day of thawing and transfer indication

• thawed blastocyst cycle cancelled before ET

• other than easy one best quality frozen/thawed blastocyst transfer (at least grade 3BB)