Impact of ovarian hyperstimulation on the luteal phase.

The contemporary approach to ovarian stimulation in IVF treatment results in supraphysiological concentrations of progesterone and oestrogen in the luteal phase. These sex steroids act directly and indirectly to mature the endometrium, thus influencing its receptivity to implantation. The development of endometrial receptivity is a complex process that may be altered by inappropriate exposure to sex steroids. Alterations in the oestrogen to progesterone ratio, growth factor concentrations and cell adhesion molecule profiles may occur after ovarian stimulation, potentially affecting the receptivity of the endometrium. Recent clinical IVF studies have shown that implantation rates and corpus luteum function are influenced by oestrogen concentrations during the early luteal phase. Few comparative studies have been performed, but after ovarian stimulation there is a reduced implantation rate and a higher pregnancy loss rate before pregnancies can be detected clinically compared with natural cycle conceptions. Novel approaches to ovarian stimulation aimed at achieving a more physiological luteal phase endocrinology are now being developed. Data from a recent pilot study by our laboratory, involving minimal ovarian hyperstimulation and no luteal phase support, are discussed.