This study is planned to enrol 30 female subjects from 1 centre in Taiwan. Each subject can receive up to 3 treatment cycles. Before undergoing a controlled ovarian stimulation with Gonal-f, a thorough gynaecologic and endocrinologic evaluation of the subject will be performed and the subjects will be given the first administration of Gonal-f low dose step up regimen for the controlled ovarian stimulation at the baseline visit. The objective of the Gonal-f therapy is to develop a single mature graafian follicle from which the ovum will be liberated after the administration of hCG. If a subject fails to respond adequately after 4 weeks of treatment, the cycle will be abandoned and the subject would recommence the treatment at a higher starting dose than in the abandoned cycle. If an excessive response is obtained, treatment would be stopped and hCG administration will be withheld and in the next cycle the treatment would start at a dosage lower than that of the previous cycle. Each enrolled subject will be followed up until the confirmation of her pregnancy status.