Ordinarily, between the sixteenth and twentieth weeks the physician is able to establish pregnancy on an absolute basis. Three important and definite signs develop; on the strength of any one of them the physician can be certain that his patient is pregnant. These signs are considered indisputable, since no other condition save pregnancy causes them. The three are: the examiner’s perception of the movements of the, the sounds of the fetal heartbeat, and the detection of the fetal skeleton by X-ray.
Movements of the Fetus Felt by the Physician
Fetal movements are divided into active and passive. The active movements can be elicited when the examiner places the flat of his hand over the lower abdomen. If the fetus moves, it feels as if something were squirming under a cover; in more advanced pregnancy there are soft, well-defined blows against the examiner’s palm. The quiescent fetus may be stimulated to move if the examiner suddenly indents the abdomen with his fingertips; the jolted fetus reacts to this indignity by squirming. It is said that active fetal movements can also be elicited by placing a piece of ice on the abdomen; I have never made the experiment. Some of the early nineteenth-century obstetricians asserted that fetal movements could be more sensitively appreciated by the cheek than by the hand.
The passive movements of the fetus depend on the fact that the fetus floats about the cavity of the uterus in a sea of fluid, the amniotic fluid. This fluid is actually present in the very first few days of pregnancy, even before the fetus is formed, and, as the fetus grows, the fluid increases in quantity. When the examiner gives the abdomen a sudden thrust with his fingers the fetus recoils like a piece of ice in a glass, which, pressed upon, sinks and then slowly rises to the surface—or like an apple when one is bobbing for it on Halloween. The passive movements of the fetus are known as ballottement. Both ballottement and active fetal move- ments can sometimes be made out on vaginal as well as abdominal examination.
The Fetal Heart
Contractions of the heart muscle of the fetus begin within a month following conception, but the heart sounds remain inaudible through the mother’s abdominal wall before mid-pregnancy. When first heard, the baby’s heart sounds are found just below the mother’s navel; later they are more readily auscultated (heard) toward one side or the other. When the fetus is large enough for the doctor to outline exactly its form and position, he listens for the fetal heart tones in the area overlying the baby’s back, in the region between the shoulder blades. The fetal heart can be heard with the naked ear, but it sounds much louder through a stethoscope, particularly if the stethoscope is of the special obstetrical variety and is held in place by a metal headband which allows not only air conduction of sound waves but also bone conduction. The fetal heart has a double beat like the tick of a watch, only its rate is more rapid and it has a soft, non-metallic pitch. The fact that the mother’s heart beats much more slowly, allows differentiation of the fetal heart from the maternal arterial pulse also heard through the mother’s abdomen as her blood courses through the large arteries of the uterus.
A common and curious lay misconception is that a pregnant woman can occasionally feel the baby’s heart pulsate as she lies on her back. She actually senses the beats of her own aorta, the largest artery in the body, as the pregnant uterus overlies and slightly compresses it. Finding the pulsation relatively slow and synchronous with her own pulse should convince the most ardent skeptic.
In addition to its value in the diagnosis of pregnancy, the fetal heart gives other important information. Normally it beats at the rate of 120 to 160 per minute; the average in six hundred cases was 136. If during pregnancy or labor the rate slows drastically and at the same time becomes irregular it is evident that something is wrong with the fetus, and appropriate remedial measures must be undertaken at once. Then, too, it is helpful in the diagnosis of twins, for in that case two separate heartbeats are often heard. In the middle of the nineteenth century it was believed that the rate of the fetal heart differed markedly in the two sexes. A rate of 124 or less was supposed to indicate a boy, and a rate of 144 or more a girl. Unfortunately, this, like most other methods of detecting the sex of the unborn, does not work.
X-rays penetrate soft body tissues and cast no shadow; it is only when they are arrested by a radio-onaque substance that a shadow is produced on the film. The chief mineral in bone is calcium, which is relatively opaque to X-rays, and, because of this, bone can be clearly and sharply outlined. The fetal skeleton is at first a framework of cartilage or gristle that is too soft to be detected by X-rays. The cartilaginous skeleton is gradually converted into bone (ossification) by the cumulative denosit of calcium, and when this occurs the skeleton can be demonstrated radiogranhicallv. The process of ossificat’on begins first in the collarbone during the sixth week of pregnancy. The visibility of bones by X-rays depends unon the amount of calcium they contain, and in the fetus this amount is too little until about the twelfth week. If conditions are ideal—very modern technical eauinment. and a thin patient—the fetal shadow can be seen this early; however, in the average case it is unusual to get a positive result until the sixteenth or eighteenth week. A positive X-ray picture of the fetus is as irrefutable evidence of pregnancy as is the physician’s detection of movements of the fetus or the beat of the baby’s heart.
In addition to the diagnosis of pregnancy, X-rays serve many other purposes in obstetrics. By means of them we can determine the size and position of the fetus in the uterus, and the size of the anerture in the mother’s bones through which the child must pass. Occasionally we can demonstrate abnormalities of the fetus before birth and sometimes determine whether the ch;ld is alive or dead in the uterus. One of the most dramatic uses is in the diagnosis of twins or triplets; we see a fetal skeleton for each. A special variety of X-ray—soft-tissue X-ray—is used in an attempt to locate the exact position of the afterbirth in cases of bleeding during the last third of pregnancy. Frequently the X-ray either rules out or creates grave suspicion that a very low insertion of the placenta in the ute^u is the cause of such bleeding, a condition called placenta praevia.
When early diagnosis of pregnancy is important, and when the physical findings are inclusive or confirmation is needed, a pregnancy test may be performed. For convenience this is usually carried out with the patient’s urine, but other body fluids such as blood and spinal fluid also give a positive pregnancy reaction. The positive reaction is due to the presenoa of a specific hormone or chemical produced by the placenta, which passes into the mother’s blood and from her bloodstream into other body fluids.
Technique of Collecting the Test Urine
The patient is instructed to take no drugs, sedatives, orbeverages the evening before collection of the urine specimen, as these substances, when excreted into the urine, are often toxic to the test animals. The patient empties her bladder before retiring and collects in a clean bottle (not necessarily sterile) three ounces of the first urine voided upon arising the next morning. When possible the specimen should be delivered to the laboratory the same morning; if delay is unavoidable, the urine should be kept refrigerated to minimize bacterial growth and loss of chemical potency.
The first satisfactory pregnancy test was devised by Asch-heim and Zondek in 1928. Although modern biological tests for pregnancy are almost never carried out by the original technique described by these pioneer investigators, numerous modifications having been developed, they are referred to generically as A-Z tests.
The test animals in common use include the mouse, rat, rabbit, South African clawed toad (Xenopus), and American frog (Rana pipiens). Both the rat and mouse tests use twenty-one-to-thirty-day-old immature female animals and are based on the appearance of blood, or hemorrhagic follicles, in their ovaries after the injection of urine from a pregnant woman. At first it took three days before the result could be read, but, by certain modifications, a yes or no can now be gotten in twenty-four hours. The rabbit test is rarely used any more because of the expense of the animals. When a South African toad is used, the test urine is injected beneath the skin, and when the test is positive freshly extruded frog eggs are found at the bottom of the cage twelve hours later. When it is negative, the test animal fails to ovulate. If the American frog is used, urine is injected into male animals, the end point being the release of spermatozoa into the cloaca. Fluid is removed with a pipette from the cloaca and examined microscopically for sperm cells; if they are found, the test is positive.
Results of Pregnancy Tests
The biological tests for pregnancy discussed above are more than 95 per cent accurate when carried out several days after the first missed menses. In earlier stages of pregnancy positive results are often obtained, but the percentage of accuracy is lower. A positive reaction is always significant; a negative test has little significance until the patient is a full two weeks overdue. False negative reactions may occur even later; the test is therefore repeated if the negative result does not agree with the clinical impression of pregnancy.
A positive pregnancy test indicates only the presence of actively secreting fetal placental tissue in the patient’s body; it does not necessarily mean a living embryo. Rarely the test is positive in conditions other than normal pregnancy, in tubal pregnancy, in a condition called hydatidiform mole (a pregnancy, ordinarily without a fetus, which is so abnormal that the placenta resembles clusters of grapes more than the usual afterbirth, hence the term, derived from the Greek word for ‘grape’), or when, as occasionally happens, the placental tissue continues functioning even though the fetus has died. However, in 99 per cent of the cases a positive test means a normally developing conception.
Short cut chemical and drug tests for pregnancy are to date not wholly reliable, despite all passing ballyhoo to the contrary.
Very rarely a nonpregnant woman may experience all the symptoms and many of the minor discomforts of pregnancy, including absence of menses, breast changes, nausea and vomiting, and swelling of the abdomen—the latter resulting from gaseous distention of the bowel. Despite medical assurance to the contrary, the patient steadfastly insists that she is pregnant and at the end of ten lunar months may even feign the pangs of labor. This condition, known as pseudocyesis, or false or spurious pregnancy, occurs predominantly in emotionally unstable, childless women with an intense longing for a baby. Pelvic examination in cases of spurious pregnancy reveals a normal-sized uterus, and the pregnancy test, of course, is negative. Treatment consists of sympathetic but positive explanations, with proof, such as a negative X-ray for the fetal skeleton. If these measures fail, psychiatric help is necessary.