The intention is to determine the serum concentration of HE4 and CA-125 in serial samples in 20 women undergoing IVF stimulation. Samples will be taken following GnRH agonist suppression, 2-3 times during FSH stimulation, at ovum pick up and two weeks following embryo transfer at the time of the hCG-test. The ovarian follicle count and the serum estradiol concentrations are recorded throughout the treatment. The serum biomarker HE4 is expected to ba a stable marker, which does not respond significantly to hormonal stimulation.