Fertilization occurs in the fallopian tube, and the very early embryo remains in the fallopian for two or three days before being propelled into the uterus by the fallopian tube. This occurs primarily as a result of the efforts of the microcilia, or small hair-like projections, on the surface of the cells that line the fallopian tube. If the early embryo is not propelled into the uterus, development can continue and implantation into the wall of the fallopian tube, rather than into the lining of the uterus, can occur. The reasons that embryos are not properly propelled into the uterus are not always clear, but are most often related to damage to the microcilia as a result of prior infection or insult.
The fallopian tube is by far the most common site of ectopic pregnancies, or pregnancies in sites other than the uterine cavity. Whereas the uterus is a distensible organ capable of expanding to hold a full-term pregnancy, the fallopian tube certainly is not. It is an organ that has very little capacity for enlargement. As the pregnancy begins to grow, its size quickly exceeds the capacity of the tube to enlarge and the tube will often rupture. This is the most significant consequence of a tubal pregnancy and can be a life-threatening event. Every effort must be made to diagnose and treat ectopics pregnancies as early as possible. (The methods by which an ectopic pregnancy can be suspected and diagnosed are discussed below.)
The two most commonly used forms of treatment for ectopic pregnancies are surgical removal and medical therapy with a drug called methotrexate. Surgical removal can be performed by laparoscopy in the majority of cases, and major surgery for this purpose is rarely required. Through the laparoscope, the surgeon can visualize the pregnancy within the tube and decide upon the best means of removal. If the ectopic has ruptured through the tube and significant bleeding has occurred, or if there has been severe damage to the tube, removal of the portion of the tube containing the ectopic may be necessary; otherwise, a more conservative procedure called a salpingostomy may be adequate. In this procedure, the surgeon makes a small incision in the fallopian tube over the site of the pregnancy and removes it, attempting to leave the tube intact. Recovery from either of these procedures is the same as for any other minor laparoscopic procedure.
If an ectopic is diagnosed early enough that the physician is not concerned about the possibility of imminent rupture, treatment with methotrexate is an option. The obvious advantage of this approach is that it avoids surgery. Methotrexate is a medication that has been extensively used as a chemotherapy agent, but pregnancy tissues are particularly sensitive to the effects of methotrexate. Therefore, very small doses of methotrexate with minimal, if any, side effects can be used and result in the cessation of growth by the pregnancy. The tissues of the ectopic pregnancy are then reabsorbed by the body.
When ectopics are treated conservatively, either by salpingostomy or methotrexate, care must be taken to be certain that the hCG levels continue to decline and return to zero. Pregnancy should be avoided for at least the next two or three months. The general incidence of ectopics is one to two percent of all pregnancies. The chances of an ectopic are obviously increased in someone who has had a prior tubal infection or prior tubal surgery. Following one prior ectopic, the chances of another ectopic increase to about 10 percent, and after two ectopics the chances of another may be as high as 30 to 35 percent.