The absence of a peak in luteinizing hormone (LH) is the primary distinction between a natural and an artificially manufactured cycle. The LH peak may have clinical significance, and activating LH/hCG receptors in the endometrium may enhance embryo implantation, as these receptors were found to express in human endometrium and experimental evidences also suggested the beneficial role of hCG in embryo implantation. Human chorionic gonadotropin is discussed in this review article for its function in secretory transformation during cycles of frozen-thawed embryo transfer