Monitoring ovarian stimulation for in vitro fertilization (IVF) and intracytoplasmatic sperm injection (ICSI) can be simplified by reducing the procedure to measuring follicles by ultrasound. Proponents of a simplified procedure claim that the procedure can be reduced to simple monitoring by ultrasound while maintaining results (numbers of mature oocytes, percentage of pregnancy and live birth rates). On the other hand simultaneous blood sampling for measuring hormone levels is still the state of the art in many clinics. A large review (Cochrane review) stated that "although there was no clear evidence for a better outcome, combined cycle monitoring was still recommended until it could be proven that ovarian hyperstimulation can be avoided without hormonal monitoring". Investigators therefore perform a study that compares the results between 2 groups: those with ultrasound monitoring and those with combined monitoring. Deciding when to plan the retrieval of the oocytes can depend on subtle differences in the number of large follicles measured by ultrasound, but also on hormonal levels in the blood of the patient. Therefore the investigators planned a randomized study in the group of patients with combined monitoring. The investigators examined if delaying the moment for planning the moment of oocyte retrieval by 24 hours had any effect on the number of mature oocytes and pregnancy rates and what the effect of rising progesterone levels might be. The investigators hypothesis was that combined monitoring could lead to better results since recent studies have thought that rising progesterone levels, if found, have a negative impact on pregnancy rates. On the other hand the investigators expect to find that waiting for larger follicles in cases with normal progesterone levels lead to a better oocyte yield.

inclusion criteria:

• absence of ovarian cysts
• both ovaries present

exclusion criteria:

• ovarian cysts
• not both ovaries present