The purpose of study is to compare the effectiveness of the Day-5 fixed administration of GnRH antagonist versus flexible administration of GnRH antagonist during ovarian stimulation in Chinese women with predicted high ovarian response, and the hypotheses is that the number of oocyte retrieved in fixed protocol is not inferior to GnRH antagonist flexible protocol.

The investigator will be responsible for analyzing the study data. This study is designed as an open-label fashion, and thus, no blindness will be maintained during the study. The database will not be locked until medical/scientific review has been completed, protocol violators have been identified, and data has been declared complete.

Statistical Methods For the primary endpoint, mean and standard deviation (SD) on the number of oocytes will be presented. The between-group difference and corresponding 95% confidence interval (CI) (Day-5 fixed protocol - flexible protocol) will be calculated by using a two-sample t-test under the assumption that the sample data are normally distributed. A test for normality will be performed prior to the analysis on primary endpoint and possible nonparametric adjustment will be made for skewed data in terms of primary analyses. The non-inferiority will be established if the lower bound of the 95%CI in the treatment difference between two groups (Day-5 fixed protocol - flexible protocol) does not exceed -3.0. The superiority may be claimed for the Day-5 fixed protocol if the lower bound of 95%CI for the treatment difference is above 0.0.

For the secondary endpoints on categorical variables, the number and percentage of the event will be calculated and displayed. Clinical and ongoing pregnancy rates will be separately calculated and presented. Between-group comparisons will be made by Chi-square test and the corresponding 95%CI will be presented by using Miettinen-Nurminen method if the number of the observed events is at least 4. Mean and SD will be summarized for continuous variables in terms of secondary outcome measures. A treatment difference between study groups will be made by using two-sample t-test or nonparametric test whenever appropriate.

The number of subjects who have reported adverse experiences (AE) and the incidence of individual AEs will be counted and presented. Fisher's exact test will be performed to compare between treatment groups.

Demographics and the subject's relevant medical history will be summarized by descriptive statistics.

All statistical analyses will be two-sided and at a significant level of a p value less than 0.05, unless otherwise specified.

Sample Size:

A sample size of 200 (1:1 allocation) achieves 80% power to detect non-inferiority of the Day-5 fixed-dose regimen as compared with the flexible protocol by a margin at -3 oocytes retrieved (3 oocytes fewer than the controlled group), using a one-sided, two-sample t-test with Mann-Whitney test adjustment at the significance level at 0.025. The true difference between the means is assumed to be 0.0 and the standard deviation of both intervention arms to be 6.8. The pre-mature discontinuation rate is set at approximately 15% for this study.

Inclusion Criteria:

1. Have an indication for COS and IVF/ICSI;

2. be <35 years old;

3. have a BMI of 18-25kg/m2;

4. have a regular menstruation with a range of 24-35 days;

5. fulfill one of these three criteria as follow:

   • the number of oocytes retrieved>15 in previous COS cycle;
   • Serum AMH (examined on the menstrual cycle day 2)>3.52ng/ml;
   • antral follicle count (AFC) (examined by ultrasonic on the menstrual cycle day 2)>16

6. have willingness to give informed consent

Exclusion Criteria:

1. Presence of unilateral ovary absence;
2. Any difficulty on oocyte pick-up with abnormal condition of ovary and pelvic cavity;
3. Women have any clinically relevant pathology could impair embryo implantation or pregnancy continuation (uterine malformation, intermural uterine fibroids>3cm, intrauterine adhesion,etc);
4. Women with polycystic ovary syndrome (PCOS) diagnosed by Rotterdam consensus criterion(Rotterdam, 2004)
5. Other known abnormal ovulation disorders (including but not limited to adrenal gland disease, thyroid disease and hyperprolactinemia);
6. A history of recurrent miscarriage or previous IVF cycles failure>2;
7. A history of ovarian hypo-response in previous ovarian stimulation;
8. Women with other clinical/socio-economic factors precluding the completion of the study at the discretion of the investigator.