First, those with bad quality and then those with moderate quality are started to be eliminated. Thus, the embryos with best quality developed for that month remain at the end.
That is why the chance of pregnancy is higher in the 5th, 6th day embryo transfer, called blastocyst transfer. But proceeding until the 5th day would not make sense in a woman with 2-3 oocytes. Because when the embryos are eliminated, an embryo to be transferred may not be left.