 Statistics of PCOS patients like age, BMI index and others would be collected. Through distributing questionnaires and query of past cases and collecting data recorded during the ovulation process like monitoring fluctuations in blood and ultrasonic monitoring results, researchers obtain the risk factors of the occurence of Ovarian Hyperstimulation SyndromeOHSS in IVF-ET treatment in PCOS patients and set up an OHSS prediction model, choose controllable factors in order to make up guidance and have intervention on patients with PCOS accordingly. The investigators expect this could improve the success rate of IVF-ET treatment in patients with PCOS, provide clues and assist to reduce the risk of the therapy. 