The reason why it is possible to get pregnant is because the medication is given in the middle of the luteal phase when the injection is given, and there is a possibility of pregnancy because ovulation has already occurred. Another reason is that GnRH-a, a gonadotropin-releasing hormone agonist, has a flare-up effect on the pituitary gland, and the initial injection may stimulate the pituitary gland to produce FSH hormone, thus promoting follicle development. Once the follicles are mature, pregnancy is possible, so contraception is needed during the descending period. If pregnancy occurs during the down regulation, there may be suppression of pituitary function leading to luteal insufficiency, increasing the possibility of miscarriage. Moreover, if pregnancy occurs during the descending period, it is necessary to keep the pregnancy under treatment.