The purpose of the present study is to analyse if corifollitropin alfa, an agent for prolonged ovarian stimulation, administered from day 4 can be clinically used instead of day 2 onwards for a controlled ovarian hyperstimulation (COH) in an antagonist protocol.

Corifollitropin alfa is a new recombinant gonadotrophin with sustained follicle-stimulating activity. It offers novel and effective treatment option for potential normal responder patients undergoing ovarian stimulation with GnRH antagonist co-treatment for IVF or in vitro fertilisation resulting in a high ongoing pregnancy rate, equal to that achieved with daily rFSH. Normally, this medication is started on day 2 of the cycle. In the present randomised trial, we want to evaluate whether this agent can be clinically used when started on day 4 of the cycle.

Inclusion Criteria:

• < 36 years old on day of randomisation
• FSH < 12 (in the early follicular phase)
• Normal ultrasound scan, i.e. presence of both ovaries, without evidence of abnormality within 6 months prior to randomisation.
• Regular menstrual cycles of 21-35 days, presumed to be ovulatory.
• BMI ≤ 29
• Weight > 60 kg
• < 3 previous trials
• ICSI
• Randomisation at out-patient clinic

Exclusion Criteria:

• ≥ 36 years old on day of randomisation
• Endometriosis ≥ grade 3
• PCOS
• Poor responders (development of < 4 follicles in a previous IVF/ICSI cycle)
• Endocrine or metabolic abnormalities (pituitary, adrenal, pancreas, liver or kidney)