To analyze the role of vascular endothelial growth factor (VEGF) and its naturally occurring circulating antagonist, soluble VEGF receptor-1 (sVEGFR-1), in infertility. VEGF is a key angiogenic factor in the endometrial and ovarian cyclic processes that are crucial for fertility and sVEGFR-1 impairs its function and fertility in animals - less is known as regards human fertility.