It normally takes the newly fertilized ovum 7 days to reach the cavity of the uterus after which it embeds itself in the endometrium. If for some reason the ovum has not reached the cavity of the uterus by the 7th day after fertilization it will embed within the Fallopian tube and become a tubal or ectopic pregnancy. Such pregnancies are rare, occurring approximately once in every 350 pregnancies. An ectopic pregnancy, however, cannot survive because it does not have the required blood supply nor is it protected by the thick muscular walls of the uterus. As the pregnancy grows and distends the Fallopian tube it may cause some lower abdominal discomfort or pain. The first indication that something is going wrong may be the onset of pain low down on one side of the abdomen. This is due to the Fallopian tube contracting in response to the stretching caused by the growing pregnancy within its lumen. Eventually, between the 6th and 12th weeks of the pregnancy, some bleeding occurs either from the outer end of the Fallopian tube or from the Fallopian tube itself because the pregnancy has ruptured its wall. This results in quite acute and severe lower abdominal discomfort which may shortly afterward be followed by some vaginal bleeding. This condition requires urgent admission to hospital and operation. It may be necessary to remove the affected tube together with the pregnancy that it contains, or occasionally it may be possible to remove the pregnancy and repair the Fallopian tube.
In its early stages, an ectopic pregnancy cannot be differentiated from a pregnancy which is situated normally within the cavity of the uterus. It produces the same hormones as does a pregnancy within the cavity of the uterus and therefore a woman has exactly the same symptoms as she would have if the pregnancy were normally situated. However, when you attend the antenatal clinic for the first time an internal examination is performed by which the doctor will know if the pregnancy is normally situated in the uterus.
Women who have had one ectopic pregnancy and have had one Fallopian tube removed are naturally worried in case they develop an ectopic pregnancy in the other Fallopian tube. This is very rare but does happen in approximately 10 percent of those women who have already had one ectopic pregnancy. If you have already had one ectopic pregnancy, as soon as you know you are pregnant you should visit the antenatal clinic so that you can be examined to check that the pregnancy is in the right place. Ultrasound scanning will confirm this.
Secondary abdominal pregnancy
On very rare occasions an ectopic pregnancy survives for an indefinite length of time. This is peculiarly common amongst South African Negroes. The fertilized ovum embeds itself in the Fallopian tube and begins to grow without rupturing the tube until about the 7th or 8th week when the chorionic tissue surrounding the pregnancy gradually erodes its way through the wall of the Fallopian tube. This usually results in the death of the pregnancy and fairly extensive internal bleeding, causing pain. Very occasionally the erosion of the wall of the Fallopian tube is so gradual that there is only slight bleeding. The chorionic tissue then protrudes through the wall of the Fallopian tube and re-embeds itself in a surrounding structure from which it obtains a new blood supply. As more and more of the chorion erodes through the wall of the tube the new area of implantation is increased to such a size that it is capable of maintaining the pregnancy. The placenta can develop on almost any organ in the pelvis, including the posterior wall of the uterus, the walls of the pelvis itself, or even the intestine. The pregnancy continues to grow and to develop and all the symptoms are those of a normal pregnancy.
A secondary abdominal pregnancy is particularly dangerous because the baby is surrounded only by the amnion and chorion which do not form a very strong protection against external injury. Rupture of the amnion and chorion results in the amniotic fluid spreading throughout the abdominal cavity and consequently peritonitis. The diagnosis of an extrauterine pregnancy is extremely difficult and may only become obvious because the baby will not present normally when the pregnancy gets close to term. Suspicion may be aroused if the pregnancy fails to develop properly and is smaller than would be expected. It is occasionally possible for an extrauterine pregnancy to develop to term, and for the woman to go into a type of spurious, or false, labor which cannot, of course, result in delivery. An operation is performed to deliver the baby by opening the abdomen as soon as the diagnosis is assured. Extrauterine pregnancies are usually diagnosed by ultrasonic scan between the 12th and 30th week of pregnancy so that survival of the baby is extremely rare and in any event these babies usually suffer from congenital abnormalities, probably caused by the inadequate blood supply to the pregnancy which cannot be as efficient as that supplied to a pregnancy developing normally within the uterus. When an operation is performed for an extrauterine pregnancy, the baby is removed together with the amniotic fluid and as much of the amnion, chorion and the umbilical cord as possible. The placenta is usually left in place because its removal would result in considerable bleeding. The abdominal cavity will gradually reabsorb it over the ensuing months.