Trigger Timing in Ovarian Stimulations

Inclusion Criteria: * Age: ≥18 and \<42 years old * AFC: ≥5 and \<20 * AMH: ≥1.1 ng/mL and \<2.5 ng/mL * BMI: ≥18.5 Kg/m2 and \<29 Kg/m * First or second ART cycle * Regular menstrual cycles (between 22 and 35 days) * Two ovaries present * Planned for single or double day 3 transfer * Infertile couples scheduled for their first IVF/ICSI cycle with fixed antagonist protocol. * Informed consent obtained. Exclusion Criteria: * Women with contraindication for IVF or ICSI, such as poorly controlled type 1 or type 2 diabetes mellitus; undiagnosed liver disease or dysfunction (based on serum liver enzyme test results); renal disease or abnormal serum renal function; significant anemia; history of deep venous thrombosis, pulmonary embolus or cerebrovascular accident; uncontrolled hypertension or known symptomatic heart disease; history of (or suspected) cervical carcinoma, endometrial carcinoma or breast carcinoma; and undiagnosed vaginal bleeding. * Previous history of poor ovarian response (\<4 oocytes retrieved) with a maximal dose of OS (≥300 IU/day) or OHSS, regardless of gonadotropin dose * Known reasons for impaired implantation (i.e. hydrosalpinx, fibroid distorting the endometrial cavity, Asherman's syndrome, thrombophilia or endometrial tuberculosis) * Repeated miscarriages (\>2 previous biochemical pregnancies or \>2 spontaneous miscarriages) * Recurrent implantation failure (\>3 failed cycles with good quality embryos) * PCOS * Untreated thyroid disfunction * Administration of exogenous E2, P4 or gonadotropins in the preceding menstrual cycle * Active female smoking * Ongoing pregnancy * Women who have previously enrolled in the trial * Those unable to comprehend the investigational nature of the proposed study * either male partner or female partner has to receive donor sperm or donor eggs. * Either male partner or female partner has to receive PGD and PGS.