For patients in the "Freeze all" group all embryos of good quality are vitrified at the blastocyst stage day 5 in the stimulated cycle according to the criteria for freezing blastocysts in each clinic. The highest quality embryo is selected and marked and will be the first one to be thawed after at least one mentrual cycle that is considered as a wash out period. Embryo transfer is performed 6-7 days after hCG injection in the blastocyst transfer cycle in this group.