RICHARD T. HULL
Fertilization typically takes place high in the fallopian tube, near the point where the ovum enters the tube after leaving the ruptured follicle. From this point, passage down to the uterus usually takes two or three days. It now seems that lower points are less optimal for fertilization either because the chances for implantation in the wall of the uterus are decreased as the time of passage to the uterus is shortened or because unknown factors reduce the chances of fertilization in the lower tubal regions.
Female infertility often is the result of scarring of the fallopian tubes subsequent to infection by a sexually transmitted disease. In such cases it is not possible for the ovum to pass down the tube or for sperm to reach it. Fallopian tubes can sometimes be repaired so as to reopen them, permitting normal fertilization to occur. However, because such surgical procedures often involve removal of the scarred section and reconnection of the open ends of the fallopian tube, there may be insufficient tube for reconnection or the tube may be so shortened that it is more difficult for the ovum to pass from the ovary into the tube. Sometimes the upper portions of fallopian tubes are missing due to malformation or surgical removal as a part of treatment for cancer or other diseases.
In vitro fertilization (IVF) was developed to circumvent persistent tubal blockage. The procedure's complexity and expense prompted researchers