Embryo transfer (ET) is the transfer of valuable embryos formed after in vitro fertilization into the uterine cavity and is a crucial step in conception. Embryo transfer is categorized into fresh embryo transfer and freeze-thawed embryo transfer according to whether the embryos have been frozen at -196°C in a liquid nitrogen tank or not, and according to the number of days of development of the embryos outside the body, it is also categorized into day 3 embryo (D3) transfer and blastocyst (D5 or D6) transfer, and some patients go through complex protocols such as sequential transfers, which are decided by the doctor and the patient based on their individual circumstances. Embryo Transfer Procedure Before the embryo transfer, the patient needs to hold urine moderately to fill up the bladder, which is helpful for the doctor to observe the size, position and shape of the uterus under the ultrasound of the abdomen, and to quickly determine the direction of the transfer tube and the position of the embryo to be placed. The doctor then uses a fine transfer cannula to transfer the embryo into the uterine cavity with the assistance of an embryologist and nurse. As the transfer tube follows the natural path of the vagina-cervix-uterine cavity, in the absence of severe reproductive tract abnormalities, fibroid compression or other abnormalities, the procedure can be completed in 1-3 minutes, and the risk factor of the procedure itself is extremely low, and some patients may find that the doctor has already completed the transfer without feeling it. For some patients who have difficulty in inserting the transfer cannula, a hard core is used to assist in the transfer with minimal pain. Embryos after transfer The microdroplets that enter the uterine cavity are like small grains of rice, and the uterine cord fits tightly to hold the microdroplets securely in the uterine cavity. The embryo, smaller than the tip of a pin, yet vigorous, swims around the uterine cavity looking for a place to attach itself before implanting in the fertile lining of the uterus and developing into a fetus. Although the embryo is implanted directly into the uterine cavity, due to tubal factors, poor endothelial tolerance, and the embryo’s own factors, there are occasional cases in which the embryo wanders outside of the uterus resulting in ectopic pregnancies, which still require vigilance on the part of the patient. Outcome after embryo transfer After embryo transfer, the embryo is deposited in the endometrium and the embryonic trophoblast cells secrete human chorionic gonadotropin (HCG) into the mother’s blood. Routinely, at 12-14 days after transfer, a biochemical pregnancy, a clinical pregnancy, or a pregnancy failure awaiting the onset of menstruation is determined based on a blood test for hCG values and a subsequent ultrasound examination. Maternal factors, sperm factors, maternal and fetal immune factors, embryo’s own factors and unknown causes can affect the outcome of embryo transfer. Some concomitant factors of infertility such as obesity, hypertension, hyperglycemia, and metabolic dysfunction syndrome may increase the risk of comorbidities during pregnancy, and these patients should follow their physician’s instructions during preparation for pregnancy and intensify preventive measures to optimize pregnancy outcomes.