At present, most assisted reproduction centers in China use descending regulation protocols with fresh embryo transfer, thus leading to complex drug regimens, high drug costs, many injections, increased incidence of moderate to severe ovarian hyperstimulation, high ovulation promotion cancellation rates, unsuitable for patients with low ovarian reserve, and supraphysiologic doses of hormone levels that may lead to increased incidence of ectopic pregnancy, preterm delivery, etc. Shanghai Jiu Hospital proposed a new strategy of IVF treatment with frozen embryo transfer as the core, the core of which is: whole embryo freezing in egg retrieval cycle, mainly using non-descending regulation ovarian stimulation protocol (i.e. using natural cycle, microstimulation, HMG + clomiphene, HMG + letrozole, luteal phase ovulation promotion, etc.), and short-acting gonadotropin agonist instead of hCG to induce ovulation. Since March 2011, the Department of Assisted Reproduction of the Ninth Hospital has been implementing whole embryo freezing and frozen embryo transfer in egg retrieval cycles, and the clinical pregnancy rate has been maintained at 40.7-51.5% without severe ovarian hyperstimulation, and the incidence of ectopic pregnancy (the probability of ectopic pregnancy in the population with frozen embryo transfer) is 2.1%. Frozen embryo transfer increases the cumulative pregnancy rate, reduces the risk of multiple pregnancies in in vitro fertilization cycles and reduces the incidence of moderate to severe ovarian hyperstimulation syndrome, and is relatively simple and easy for patients to perform. The use of letrozole for ovulation and non-injectable progesterone (oral + vaginal plugs) in the hormone replacement regimen has been pioneered in China to reduce patient pain and increase the pregnancy rate of frozen-thawed embryo transfer. Clinical pregnancy rate of frozen embryo transfer in Jiu Hospital from January to June 2012. January: 47.7% February: 46.4% March: 51.5% April: 50.5% May: 50.5% June: 51.3% Clinical pregnancy rate of frozen embryo transfer in Jiu Hospital from March to December 2011. March: 42.9% April: 41.7% May: 40.7% June: 46.6% July: 45.8% August: 46.2% September: 40.9% October: 47.5% November: 48.5% December: 43.1%