- Study 2 "The cardiovascular profile in female subfertility": The cardiovascular profile of women with female subfertility classified as unexplained subfertility or "expected" decreased ovarian reserve compared to fertile women. For this study 4 measurements will be performed: the uterine artery pulsatility index (PI) as measure of uterine perfusion, the plasma volume as measure of venous reserve capacity, the intima media thickness of the carotid arteries as proxy of chronic strain and the endothelial function, measured by flow mediated dilatation (FMD) of the brachial artery.