In this study all patients who will undergo frozen embryo transfer are randomly allocated to be prepared for transfer by using either natural cycle (with or without hCG for ovulation induction) or Hormonal cycle (with or without administration of GnRH-a) In natural cycle without hCG, daily monitoring of urinary LH is started from day eight of the cycle and frozen-thawed embryo transfer is planned 3-5 days after detection of LH surge, observing mature follicles in ultrasound and endometrial thickness over 7mm for cleavage embryos.