Abnormal changes in pregnancy

Ectopic pregnancy

An ectopic pregnancy is one in which the conceptus (the products of conception—i.e., the placenta, the membranes, and the embryo) implants or attaches itself in a place other than the normal location in the lining of the upper uterine cavity. The site of implantation may be either at an abnormal location within the uterus itself or in an area outside the uterus. Ectopic pregnancies outside the uterine cavity occur about once in every 300 pregnancies. They are one of the major causes of maternal deaths.

Normally an ovum or egg passes from the ovary into the tube, is fertilized in the tube, and moves downward into the uterus. It buries itself in the lining of the upper part of the uterine cavity. It may pass farther down and attach itself to the lining of the mouth of the uterus (the cervix), creating a cervical pregnancy. These are rare and cause severe vaginal bleeding; the conceptus is expelled or discovered within a few months after implantation.

If a conceptus attaches itself to the lower part of the uterine cavity, it is a low implantation. When a low implantation occurs, the placenta grows over the cervical opening, in a formation called a placenta praevia. This causes the woman to bleed, often profusely, through the vagina, because the placenta tears as the cervix begins to open during the latter part of pregnancy.

When the fertilized egg implants in the narrow space or angle of the uterine cavity near the connection of the uterus with the fallopian tube, it is called an angular pregnancy; many angular pregnancies terminate in abortions; others go to term but are complicated because the placenta does not separate properly from the uterine wall after the birth of the baby. An angular pregnancy differs from a cornual pregnancy, which develops in the side of a bilobed or bicornate uterus.

Implantation in the narrow part of the fallopian, or uterine, tube, which lies within the uterine wall, produces what is called an interstitial pregnancy. This occurs in approximately 4 percent of ectopic pregnancies. An interstitial pregnancy gradually stretches the wall of the uterus until—usually between the 8th and 16th week of gestation—the wall ruptures in an explosive manner and there is profuse bleeding into the abdomen.

Most persons associate ectopic pregnancies with tubal pregnancies, because most ectopic pregnancies occur in the uterine tubes. The tube beyond the uterus has three parts: the isthmus, a narrow section near the uterus; the ampulla, which is wider and more dilatable; and the infundibulum, the flaring, trumpetlike portion of the tube nearest the ovary. A tubal ectopic pregnancy is designated by the area of the tube in which it is implanted. An isthmic pregnancy differs from one in the ampulla or infundibulum because the narrow tube cannot expand. Rupture of the affected tube with profuse intra-abdominal hemorrhage occurs early, usually within eight weeks after conception.

Ampullar pregnancies, which are by far the most common, usually terminate either in a tubal abortion, in which the embryo and the developing afterbirth are expelled through the open end of the tube into the abdomen; by a tubal rupture; or, less commonly, by absorption of the conceptus.

Sometimes the tube ruptures into the tissues attaching it to the wall of the pelvis, producing an intraligamentous pregnancy. Rarely, the embryo is expelled into the abdomen and the afterbirth remains attached to the tube; the embryo lives and grows. Such a condition is referred to as a secondary abdominal pregnancy. Primary abdominal pregnancies, in which the fertilized egg attaches to an abdominal organ, and ovarian pregnancies are rarer still.

It is generally believed, but not proved, that most tubal pregnancies are caused by scars, pockets, kinks, or adhesions in the tubal lining resulting from tubal infections. The infection may have been gonorrhea; it may have occurred after an abortion, after the delivery of a baby, or after a pelvic surgical operation; or it may have been caused by appendicitis. Kinking, scarring, and partial adhesions of the outside of the tube may be the result of inflammation following a pelvic operation or of an abdominal inflammation. Tubes, defective from birth, may be too small for the passage of the conceptus or may be pocketed or doubled with one tubal half forming a blind pocket. There may be areas in the tubal lining that behave like the lining of the uterus (they show a decidual reaction that is conducive to implantation) so that they offer a favourable spot for the fertilized egg to implant. Pelvic tumours may distort the tube and obstruct it so that the conceptus cannot move downward. Theoretically, endocrine disturbances may delay tubal motility.

Whatever the cause, when a tubal implantation occurs, it may be assumed that either migration of the fertilized egg within the tube was delayed by an extrinsic factor so that the egg grew to the point where it should implant or that the mechanism for implantation within the egg itself was prematurely activated in the tube. One or the other of these causative factors can sometimes be seen when a woman is operated upon for an ectopic pregnancy. In a great number of cases, however, no tube abnormality can be found. There is no satisfactory explanation for most abnormal implantations in the uterus, although defective uterine structure has been noted in some cases.

Primary abdominal and ovarian pregnancies can best be explained by a mechanism in which the fertilized ovum is swept out of the tube by a reverse peristalsis of the tube, but it is quite possible that, in rare instances, the ovum and spermatozoa meet and fertilization and implantation take place within the abdomen.

Ectopic pregnancy is frequently mistaken for other disorders. Typically, but not invariably, the woman who has an ectopic pregnancy in the ampullar part of the tube will have missed one or two menstrual periods. She need not have other symptoms of pregnancy. She has felt enough discomfort in the lower part of her abdomen to lead her to consult a physician. She has had recurrent episodes of rather light, irregular bleeding from the vagina. She has felt weak or faint at times. The signs of pregnancy are not likely to be present, and results of a pregnancy test are more often negative than positive. The physician, on pelvic examination, feels a tender, soft mass in one side of the pelvis. At this stage the differentiation must be made between an ectopic pregnancy and an intrauterine pregnancy with abortion, acute appendicitis, intestinal colic, inflammation of a fallopian tube, and a twisted ovarian tumour. Unless the diagnosis can be made, the patient continues to complain for several more days and then has a sudden severe pain and collapses from brisk bleeding within the abdomen.

Sudden and acute abdominal pain and collapse due to severe hemorrhage are only rarely the first signs that something is amiss. If this does happen, it is usually because implantation has occurred in the isthmic portion of the tube and hemorrhage and tubal rupture occur simultaneously. More frequently, a woman has missed one menstrual period, has a sensation of pelvic pressure, feels that she must urinate, and collapses in the bathroom. She may be unconscious and pulseless from loss of blood when she arrives at the hospital.

Interstitial pregnancies are often mistaken for intrauterine ones, but the patient has pain and may have intermittent vaginal bleeding. After several months she has sudden, severe pain, collapses from a massive intra-abdominal hemorrhage, and may die before surgical help can reach her. Most of the women who die from ectopic pregnancies do so from interstitial ones.

Combined pregnancies, in which there is an ectopic pregnancy and a normal one in the uterus, or a fetus in each tube, have occurred and have compounded the difficulty in making a diagnosis. In a number of instances, the ectopic conceptus has been removed without complications, and the uterine fetus has progressed to term.

Not all ectopic pregnancies end with a catastrophic hemorrhage and collapse. In a few instances tubal, abdominal, and broad ligament pregnancies have gone on until a living baby was obtained at the time of operation. In other cases the fetus died and, if very young, was resorbed; in others, when the fetus was larger, death was followed by absorption of the fluid in the sac, and the fetus was gradually converted into a more or less mummified mass. Some ectopic pregnancies of this type have caused no symptoms and have been carried by women for years. Undoubtedly many ectopic pregnancies that are in an early stage when they are expelled emerge through the open end of the uterine tube, are resorbed, and are never recognized.

Once diagnosed, the treatment of ectopic pregnancies outside the uterine cavity is almost always a matter of prompt surgical intervention with proper attention to replacement of blood and fluid.