Corpus luteum-resistance index (CL-RI) of each corpus luteum of each patient in the treatment groups. Twenty-four patients who underwent AIH under the standardized ovarian-stimulation protocol with GnRHa were recruited in this study. Dependent on luteal supports, the patients were divided to 3 groups; 9 women were given ethinylestradiol plus norgestrel (Planovar) orally throughout the luteal phase; 8 women were given HCG 2,000 IU on days 2 and 4 after ovulation induction in addition to Planovar (HCG group); 7 women were given vitamin E (600 mg/day, 3 times per day) orally throughout the luteal phase in addition to Planovar (vitamin E group). Planovar was used as a control in this study because it does not affect luteal blood flow. Vitamin E was used to increase luteal blood flow. CL-RI was examined during the mid-luteal phase (6-8 days after ovulation). In case of patients with multiple ovulations, CL-RI was examined in each corpus luteum, and the mean was used as a patient mean value. a; p < 0.01 and b; p < 0.05 v.s. control group (Kruskal-Wallis test followed by the Mann-Whitney U-test using the Bonferroni correction).