This is because the two fallopian tubes are far apart in the pelvic cavity, especially the umbilical end of the fallopian tube. When the egg is ovulated from the ovary, it will normally be caught by the umbilical part of the fallopian tube on the same side. If it is the umbrella of the opposite fallopian tube, it is farther away from the egg and the egg itself is not mobile, so after normal ovulation, it is the ipsilateral tube that grabs the follicle on the same side to achieve pregnancy. If there is obstruction on this side of the fallopian tube, the umbilical atresia of the fallopian tube will not be able to capture the egg into the fallopian tube, which will lead to infertility.