I. High-quality oocytes are the basis of successful IVF IVF-ET cycles are usually performed with controlled ovulation promotion to stimulate the development of multiple follicles and to obtain more eggs for fertilization so that multiple embryos of high quality can be selected for transfer to improve pregnancy rates. The Spanish authors Merce LT et al. analyzed the correlation between the quality of embryos and the clinical pregnancy rate on the day of transfer after ovulation in IVF/ICSI patients and the volume and number of follicles, blood flow and elasticity of the follicular wall on the day of HCG, and concluded that the quality of follicles is a direct predictor of the quality of eggs and embryos, and therefore an adequate number of eggs of good quality is the basis and primary condition for successful IVF. Insufficient number of eggs obtained will lead to a decrease in the number of embryos available for transfer, especially the number of high quality embryos transferred, which may be one of the important reasons for IVF failure. The main causes of reduced egg production or empty follicles are: 1. impaired oocyte maturation. Several scholars at home and abroad have also reported that no oocytes were obtained after repeated COH in IVF/ICSI patients, or that oocytes with abnormal structures (oocytes without zona pellucida, degenerated oocytes, oocytes with only oocyte-like structures and zona pellucida but no oocytes, etc.) were obtained. It is speculated that this may be due to increased expression of apoptotic genes within the follicle, resulting in decreased transcriptional products essential for normal follicular growth, resulting in oocyte atresia and developmental defects. This condition may be an important cause of infertility in patients with primary infertility of unknown origin. 2. Decreased egg production may be associated with HCG. All cases in this study had sufficient HCG exposure time (34-38hr after HCG injection for egg retrieval) and the decreased or no egg acquisition may be related to the decreased biological activity of HCG in vivo. Currently, there are two forms of HCG used in clinical work, recombinant HCG (r-HCG) and urine-derived HCG (u-HCG). Some foreign scholars believe that r-HCG has a lower rate of egg acquisition after u-HCG injection because its biological stability is better than that of u-HCG, and Penarrubia et al. reported that more oocytes were obtained by switching to r-HCG, but Zhu Guijin et al. There was no significant correlation between the two doses of HCG and the occurrence of failed egg retrieval. It has been suggested that patients with a previous significant decrease in the rate of egg retrieval can be tested for HCG concentration in serum 12 hours after HCG injection, and if it is less than 10 mIU/ml, it is recommended to re-inject HCG, which can partially correct the low rate of egg retrieval due to insufficient biological activity of HCG. 3. The low rate of egg production may be related to the correct timing of HCG injection. If HCG is injected too early, the mound will be too small and tightly attached to the follicle wall, making aspiration difficult, resulting in fewer eggs being recovered and immature eggs being recovered, resulting in a low fertilization rate and contributing to follicular atresia, resulting in a low pregnancy rate; if HCG is injected too late, the follicles will be too mature before ovulation and the oocytes may degenerate, which is also detrimental to later development, resulting in the loss of oocytes in mature follicles and the loss of immature oocytes in smaller follicles. The immature oocytes obtained in the smaller follicles are not capable of fertilization. Serum E2 was monitored daily when the dominant follicle reached 14 mm in diameter during the patient’s COH, noting the relationship between E2 and P. At ≥3 follicles ≥16 mm in diameter, it was estimated that each follicle ≥14 mm in diameter had approximately 200 pg/ml of E2, and the timing of HCG injection was appropriately advanced, and significantly higher rates of egg acquisition, transferable embryos, and clinical pregnancy were obtained than in the previous cycle; further conclusions await observation with larger samples. The incidence of moderate and severe OHSS, a complication closely related to COH, did not differ from that of patients with normal egg acquisition rate. Since there was no statistical difference in the number of mature follicles on HCG day, the role of serum E2 levels in vivo in triggering OHSS was comparable. In cases with low egg acquisition rate, the cumulative pregnancy rate in such patients was not lower than in patients with better egg acquisition rate if the number of embryos obtained was higher, probably due to the exogenous administration of estrogen and progesterone to prepare the endometrium during the thawing cycle, which excludes the high estrogenic state in vivo during the COH cycle and the detrimental effect of hormones on the endometrium, and when the embryos are of better quality, which is more favorable in some patients with low egg acquisition rate. In conclusion, the rate of egg acquisition from mature follicles is predictive of pregnancy outcome in IVF/ICSI. In previous IVF/ICSI cycles, it is important to monitor the individualization of COH in patients with an egg yield of ≤50% and to improve the quality of oocytes to avoid a decrease in egg yield due to inappropriate timing of HCG injection. If the number of embryos available for transfer is sufficient, it is possible to consider no transfer or transfer of only one or two embryos during the egg retrieval cycle, and thawing and transferring frozen and thawed embryos may be one of the important methods to improve the cumulative pregnancy rate when the egg acquisition rate decreases significantly.