Gonadotropin-releasing hormone antagonists (GnRH-ant) are routinely used to prevent premature luteinizing hormone (LH) surges in women undergoing in vitro fertilization (IVF) programs. GnRH-ant act by competitively binding GnRH receptors (GnRHr), leading to rapid pituitary suppression. GnRH-ant can also block extrapituitary GnRHr, including those present in ovary, placenta, and endometrium. A full understanding of the functional roles played by extrapitutary GnRHr, along with a better characterization of the possible reproductive consequences of their blockage may aid the refinement of controlled ovarian stimulation (COS) protocols using GnRHant. This review summarizes current research in the area, especially focusing on the possible impact of GnRH-ant on steroidogenesis, folliculogenesis and endometrial receptivity.