Embryo transfer involves placing the embryo in the uterine cavity, in the middle position, roughly 1-2cm from the bottom of the uterus, on both the front and back walls. Because the embryo, when placed in the uterine cavity, is not fixed in the position in which it is placed, it will wander and choose the right place to settle, so there is a possibility of ectopic pregnancy even in IVF patients. In individual cases it is possible for the gestational sac to travel to the uterine corner or within the fallopian tube, so it is important for patients to seek medical attention when they experience abdominal pain and vaginal bleeding after the transfer. For patients who undergo a stepwise transfer, the location of the embryo transfer is relatively variable. It is done through two transfers, with the first transfer taking place relatively close to the bottom of the uterus and the second transfer of embryos relatively close to the inside of the uterine cavity. So for patients undergoing a step-by-step transfer, the timing of the embryo transfer varies and the location of the embryo transfer has to change accordingly.