When a normal pregnancy occurs, the egg released by the woman’s ovary is fertilized by a sperm in one of the Fallopian tubes, the fine tubes which conduct the egg from the ovary to the interior of the uterus. When it arrives there the fertilized egg is implanted in the lining of the uterus, which has been prepared to receive it by the hormonal changes the woman goes through before and during ovulation.
Once implanted, the fertilized egg proceeds to divide and develop over about nine months into a full-term infant ready for life in the outside world. The muscular uterus is able to expand enormously during those nine months to hold and nourish the developing fetus, and then has the strong muscles necessary to contract and deliver the baby.
Sometimes the fertilized egg does not make it into the uterus, but gets stuck in the Fallopian tube, or even wanders into the abdominal cavity. If it is able to attach itself to the lining of either the tube or the abdominal cavity, it may proceed to divide, and start to develop into a fetus. Attachment and growth of a fertilized egg in any location other than the inside of the uterus is called an ectopic pregnancy, and if the point of attachment is in the Fallopian tube, it is referred to as a tubal pregnancy.
Tubal pregnancies are very dangerous to the mother, since the tube is tiny, and cannot expand to hold the developing fetus as does the uterus. Eventually the tube will rupture, causing severe hemorrhage into the mother’s abdominal cavity, which was very often fatal in the days before we had effective treatment. The fetus always dies when such a rupture takes place, and there is no way known to preserve the fetus in such a situation.
The major symptom of a tubal pregnancy is pain low in the pelvis, and this diagnosis must always be considered in any woman of childbearing age who complains of such pelvic pain. There is often some vaginal bleeding along with the pain. These symptoms may develop before the woman has missed a menstrual period, and she may not even know that she is pregnant, although modern pregnancy tests, (not the home tests) will often diagnose the pregnancy. When examined by the doctor, the tube on one side can often be felt, which means that it is swollen, and it is usually extremely tender. An ultrasound examination can then make the diagnosis.
Until recently, surgery to remove the tube was the only treatment option. In recent years a method of treating early tubal pregnancies with methotrexate has been developed which avoids the need for surgery and spares the Fallopian tube.
It is generally assumed by doctors that tubal pregnancies are caused by a previous infection in the Fallopian tube which caused scarring and therefore interfered with the smooth passage of the fertilized egg into the uterus. Gonorrhea frequently caused such scarring, and it is now recognized that chlamydia infection, which may not cause symptoms and is therefore less often diagnosed, can also cause it. It is for this reason that doctors have become much more concerned with routinely testing for, and treating, chlamydia infections when a woman gets her routine Pap smear, or has any symptoms of a pelvic infection.
Surprisingly, the rare abdominal pregnancies may not cause pain, and the fetus can grow to full term size. Since the fetus is outside the uterus, it clearly cannot be delivered normally, and a Caesarian section is necessary. Because of bleeding complications such a pregnancy is still extremely risky for the mother, and the fetus often does not survive.