Stimulation with hCG during timing of ovulation and pregnancy state induces an increase in steroids secretion of rescue corpus luteum.In pateints who became pregnant after frozen embryo transfer/FET/, the 17-hydroxyprogesteron and estradiol levels increased, most probably reflecting the rescue of the corpus luteum by hCG secreted from trophoblastic tissue.On the contrary, in patient who did not became pregnant, the dominant ovarian volume decreased by the second measurrnent/1week after FET/and 17-droxyprogesteron were lower than in pregnant women, reflecting the continuing regression of the corpus iuteum without hCG stimulation.