Gonadotropins (Gn, e.g., hMG) combined with clomiphene (cc) is a common regimen for ovarian microstimulation. If cc is given orally first and HMG is added a few days later, it is called the cc + hMG regimen; conversely, if hMG is injected first and cc is added a few days later, it is called the hMG + cc regimen. From the point of view of drug administration, the two are only different in the order of drug administration, what is the difference? Let’s start with the mechanism of action of cc. cc is an estrogen receptor blocker that binds firmly to the estrogen receptor in the cell plasma, blocking the binding of estrogen to the receptor and preventing estrogen from exerting its effects. When cc acts on the estrogen receptors in the nociceptors, the nociceptors sense that the body is “deficient” in estrogen and thus, in order to compensate for the estrogen “deficiency”, the pituitary gland, under the command of the nociceptors, accelerates the secretion of the sex hormones (FSH, LH), prompting follicle development. The clinical use of cc to induce ovulation exploits this mechanism. In the cc + hMG regimen, cc is first administered orally to increase FSH and LH levels and induce early follicular development. In a sense, the cc + hMG regimen is essentially an “enhanced” version of oral cc alone to induce ovulation. In the hMG + cc regimen, hMG is used first to cause early development of multiple follicles, and as the follicles develop, estrogen levels gradually increase. Normally, the gradual rise in estrogen excites the production of luteinizing hormone (LH) until an LH peak is produced. Although the LH peak is necessary for the final maturation of the egg, a premature LH peak (premature LH peak) is a nightmare for ovulation because it causes premature luteinization of the follicle, which can seriously affect the quality of the egg. The addition of cc to “paralyze” the central nervous system’s sensitivity to estrogen and prevent the onset of the LH peak is the main rationale for the use of cc in the hMG + cc regimen. From this perspective, the hMG + cc regimen is actually similar to the gonadotropin-releasing hormone inhibitor regimen (GnRH-Ant). In summary, the endocrine mechanisms of the CC+hMG and hMG+CC regimens are different in terms of ovulation promotion. The former tends to have a weaker stimulatory effect on the ovaries than the latter, with somewhat fewer synchronized follicles developing. The latter may be more efficient in ovulation promotion.