The aim of this study is to investigate the effect of ovarian and endometrial response on live birth rates (LBRs) in young normal and high responders and prolonged pituitary downregulation on endometrial receptivity and clinical outcomes in patients with different endometrial thickness. Between January 2013 and December 2017, 9511 patients underwent first in vitro fertilization (IVF)/intracytoplasmic sperm injection (ICSI) cycles with age <= 35 years, follicle stimulating hormone < 10 IU/l, and >= 4 retrieved oocytes were conducted. The estradiol (E-2) levels on the human chorionic gonadotropin (HCG) day were classified into 4 groups: group 1 (<3000 pg/mL); group 2 (3000-5000 pg/mL); group 3 (5000-7000 pg/mL), and group 4 (>= 7000 pg/mL). Logistic regression analysis was performed to predict the independent variables for live birth. Clinical outcomes between gonadotropin-releasing hormone agonist (GnRH-a) long protocol and GnRH-a prolonged protocol in patients with different endometrial thickness (EMT) were compared. There were no significant differences among the 4 groups in implantation rates, clinical pregnancy rates, and LBRs (P > .05). Binary logistic regression analysis suggested that EMT but not E-2 levels was one of the independent predictive factors of LBRs (odds ratio 0.889, 95% confidence interval, 0.865-0.914, P < .001). The prolonged protocol had significantly higher implantation rates and clinical pregnancy rates in patients with medium (7 < EMT < 14 mm), especially thin endometrium (<= 7 mm) compared to short GnRH-a long protocol. Our study showed that endometrial response but not ovarian response was associated with LBRs in young normal and hyper responders. Prolonged pituitary downregulation was an effective treatment to improve endometrial receptivity in patients with medium, especially thin endometrium.