This study is a prospective randomized trial with 242 IUI cycles. Patients are randomized in two groups including 121 cycles in each group. A total of 255 cycles in 167 patients are finally recruited. In the first group, the patients will be treated with triptorelin (Gonapeptyl®) in their luteal phase. As for the other group, the patients will undergo the luteal phase without any supportive medication. This study is going to clarify the role of the gonadotropin agonist (triptorelin acetate, Gonapeptyl®) as a luteal phase supporter. The benefit of the treatment is measured by the numbers in the live birth and clinical pregnancy rates.