Ovarian stimulation will be started if there are no ovarian cysts on ultrasound scan. They will receive one long acting gonadotrophin injection Elonva 150 microgram subcutaneously followed by daily gonadotrophin injections (Puregon) 200 IU in an antagonist protocol. Antagonist (orgalutran 0.25 mg) will be started on day 5 of ovarian stimulation. Transvaginal ultrasound will be performed for follicular tracking 7 days after the Elonva injection and every 1-3 days thereafter. No adjustment in FSH dose is allowed. Cycles will be cancelled if there are less than 3 follicles larger than 18mm after one week of 200 IU Puregon or there no developing follicle (i.e. larger than 11mm) after one week of 200 IU Puregon.