Steps performed in IVF: Controlled Superovulation Since the length of the natural menstrual cycle varies from person to person and from cycle to cycle in the same patient, it is not easy to schedule egg retrieval, and since only one dominant follicle develops in the natural cycle, only one embryo can be formed after fertilization, and the pregnancy rate of transferring one embryo is very low. Therefore, controlled superovulation is needed to enhance and improve ovarian function in order to obtain multiple healthy eggs regardless of the natural cycle, to provide multiple embryos for transfer, and to synchronize the corpus luteum development with the endometrial function as much as possible. Controlled ovulation is usually achieved by first down-regulating FSH and LH with GnRHa and then administering HMG or FSH ovulation drugs to stimulate follicle growth in the ovaries, adjusting the dose of the drug according to the patient’s responsiveness to it. Follicle monitoring To evaluate the effect of ovarian stimulation and to determine the timing of egg retrieval, follicle size should be monitored by vaginal ultrasound and the E2 value (estrogen) should be checked with blood sampling to adjust the dosage of medication. When two to three or more follicles are larger than 1.8 cm in diameter and the number of follicles above 1.4 cm is comparable to the E2 value, human chorionic gonadotropin (hCG) can be injected to promote follicle maturation. The eggs are retrieved 34 to 36 hours after hCG injection. The most commonly used method of egg retrieval is under local anesthesia, guided by vaginal ultrasound, and the needle is passed through the vaginal vault to the ovaries to aspirate the eggs, which are immediately transferred under a microscope to a Petri dish containing embryo culture fluid and incubated in a 38.5°C incubator. Sperm retrieval Sperm retrieval is performed on the same day as egg retrieval. Hands were washed before sperm retrieval and semen was retained by the masturbation method. The small cup given is sterile and the rim and the inside of the cup should not be touched during retention. The extracted semen is processed by the upstream method or Percoll density gradient centrifugation. In vitro fertilization The treated sperm and eggs are placed in the same Petri dish 4 to 5 hours after egg collection and co-cultured for 18 hours before fertilization can be observed under a microscope. If the sperm quality is too poor for natural fertilization, fertilization must be performed by intracytoplasmic single sperm injection . Embryo Embryo culture The fertilized egg is transferred into the embryo culture solution for culture, usually for 48 to 72 hours, in order to observe is its development is normal, after this stage, it can generally develop to the 8 to 16 cell stage. Embryo transfer The number of embryos to be transferred is determined by the patient’s age, whether she has been pregnant or not, and the quality of the embryos. Embryo transfer usually does not require anesthesia. At present, most embryos are transferred 2 to 3 days after fertilization, but in our clinic, embryos are transferred 3 to 5 days after fertilization. Delaying embryo transfer requires higher conditions for in vitro culture, but delaying transfer is more in line with pregnancy physiology, and it can also eliminate poor quality embryos through natural screening, which can improve pregnancy rate and reduce multiple birth rate. Hormone supplementation after embryo transfer Currently we mostly use injections to give progesterone to support the corpus luteum. If pregnancy is confirmed, hCG supplementation is switched to continue until 10 weeks of pregnancy. Pregnancy can be determined by urine test or blood draw 14 days after embryo transfer.