In this prospective study, the investigators would like to show whether ovarian stimulation with pretreatment of a GnRH antagonist during 3 consecutive days at initiation of the cycle, is possible.

A recently accepted study demonstrated that raised progesterone levels can be normalized through administration of a GnRH antagonist during three subsequent days prior to the start of gonadotropin stimulation in a GnRH antagonist protocol. This regimen, after normalisation of the progesterone value, allows controlled ovarian hyperstimulation (COH). Since this regimen is valid in case of elevated progesterone, GnRH antagonists pretreatment may prove to be a valid tool for scheduling IVF treatment in patients with normal progesterone values on day 2 of the cycle. In this prospective randomised trial, the investigators study the impact of administration of a GnRH antagonist during 3 consecutive days at initiation of the cycle.

Inclusion Criteria:

• < 39 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 between 18 and 29 (both inclusive)
• 1st or 2nd trial
• IVF or ICSI
• Randomisation at out-patient clinic

Exclusion Criteria:

• ≥ 39 years old on day of randomisation
• Endometriosis ≥ grade 3
• PCOS