Conventional luteal phase support after human chorionic gonadotrophin (hCG) triggering in women undergoing in vitro fertilization/intracytoplasmic sperm injection (IVF/ICSI) provides adequate pregnancy rates and live birth rates, but Ovarian hyperstimulation syndrome (OHSS) still occurs in 1-3% of the patients. If gonadotropin-releasing hormone agonist (GnRHa) are used instead of hCG, OHSS does not occur, but clinical results are somehow diminished.

By testing different luteal support protocols on women undergoing GnRHa triggering, the investigators aim to find out which protocol resembles the most the gene expression profile observed after hCG triggering and conventional luteal phase support, in order to choose it as the most adequate in terms of endometrium receptivity and safety (OHSS incidence).

Inclusion criteria :

• Healthy oocyte donor women
• Aged 18-35 years
• With a menstrual cycle length of 26-35 days
• Normal ultrasound scan of uterus and ovaries
• Normal basal hormones
• No contraindication for controlled ovarian stimulation (COS)
• Willing to participate in the study and providing written informed consent.

Exclusion Criteria:

• Subjects with current or previous history of an endocrine abnormality
• Subjects with an abnormal outcome of blood biochemistry or hematology
• Subjects with an abnormal cervical smear
• Subjects with a chronic disease
• Subjects with any relevant ovarian-, tubal- or uterine-pathology that could interfere with the COS treatment
• Pregnancy
• Subjects who had a previous history of ovarian hyperresponse or ovarian hyperstimulation syndrome (OHSS), polycystic ovary syndrome (PCOS) or a basal antral follicle count (AFC) of more than 20 on ultrasound (11 mm, both ovaries combined) .
• Previous low ovarian response to FSH or hMG treatment (i.e. cycle cancelled due to insufficient ovarian response or less than 6 oocytes obtained).
• A history of recurrent miscarriage,
• Smoking more than 10 cigarettes per day.
• Not willing to comply with study procedures