 Serum E2 and the endometrial thickness were measured on the day of HCG administration. The endometrial thickness was measured in a sagittal plane in the fundus of the uterus point of maximal thickness from the echogenic interface at the junction of the endometrium and myometrium Ovulation was confirmed when midluteal day 21of the cycle serum progesterone was 5 ngmL. Serum β-hCG was determined 2 weeks after HCG injection for diagnosis of biochemical pregnancy. Sonographic evidence of an intrauterine gestational sac at 6 weeks gestation was considered an evident of a clinical pregnancy. 