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- The Prospective Mother - 4/45 -
of even more uncertain length in man than in the lower animals; but since the eighteenth century thirty-nine weeks have been accepted as the average duration of the human pregnancy when reckoned from the day of conception. As this date is seldom known, it is most convenient to reckon from the first day of the last menstrual period. Estimated in this way its average duration is 280 days. As this period corresponds to ten menstrual cycles, physicians prefer to describe pregnancy as lasting 10 lunar months of four weeks each. This is equivalent to 9 calendar months, in terms of which its duration is popularly stated.
THE ESTIMATION OF THE DATE OF CONFINEMENT.--Since pregnancy is not an absolutely fixed period, we possess no reliable means of predicting the exact day when it will end. The most satisfactory method of prediction consists in counting forward 280 days from the beginning of the last menstruation or, what gives the same result, counting backward eighty-five days from this date. _To make the calculation in the simplest way we count back three months and add seven days_; this addition is made because seven days generally represents the difference between three months and eighty-five days. If the last menstruation, for example, began on October 30th, we count back three months to July 30th and add seven days, which gives August 6th as the probable date of confinement.
A prospective mother should remember that this prediction is no more than approximate. The calculation does not give the exact date of delivery more than four or five times in a hundred cases. It is accurate within a week in half the cases and within two weeks in four-fifths. We also know that delivery is somewhat more likely to occur after the expected date than before it. But perhaps we shall get the clearest idea of the accuracy of the rule, or better still of its inaccuracy, if we imagine twenty patients to have the same predicted date, all of them giving birth to mature infants. The chances are that only one of these patients will be confined upon the day predicted; nine will be confined before and ten after it. In all probability five of those who pass the predicted day will be delivered within a week and four others within the second week, while the twentieth patient will not be delivered until three weeks or more have elapsed.
Such results clearly indicate our inability to make accurate predictions even though pregnancy is normal in every way. Whenever patients pass their expected date uneventfully, if they will bear in mind that the fault lies with the method of prediction and not with the pregnancy, they will often be saved anxiety. Frequently such discrepancies are attributable to a false assumption, for our rule always assumes that the conception took place immediately after a menstrual period. While this is generally true, the number of cases in which it occurs just before the period to be missed is by no means inconsiderable, and in these we should not expect pregnancy to end until two or three weeks after the day predicted by the rule.
Occasionally patients know the precise day upon which conception took place, and prefer to estimate the day of confinement from that rather than from the beginning of the last menstruation. They may do so by counting back thirteen weeks from the day of conception; but this method also is subject to error for, as we have noted, the duration of pregnancy reckoned in this more exact manner is not constant. Such a calculation rarely offers any advantage over that made from the menstrual record.
Another method of estimating the date of confinement is based upon the assumption that fetal movements are first perceived by the mother toward the eighteenth week of pregnancy; and in consequence twenty- two weeks generally elapse between quickening and the day of delivery. Although such a calculation is far from certain in its prediction, there are instances in which no other calculation can be made. A nursing mother, for example, may become pregnant before menstruation has been reestablished. Under these circumstances, obviously, the date of confinement cannot be estimated in the ordinary way, and it is then especially important to know the first day on which the fetal movements were felt. Furthermore, it is helpful to note this date in every case, since it serves, if for nothing more, to confirm the prediction made from the menstrual record. Besides the two methods just described, which are alike in that they require the patient herself to make the necessary observations, there is a third method of estimating how far pregnancy has advanced, by which the physician is enabled to draw his own conclusions. This method is based upon the fact that the womb enlarges from month to month during pregnancy at a constant rate. Up to the end of the third lunar month it cannot be felt through the abdominal wall; but in the course of the fourth month, on account of its size, it must rise into the abdominal cavity. At the beginning of the sixth month the top of the womb is at the level of the navel, and at the ninth reaches the ribs. The diaphragm then prevents the womb from going higher; and two or three weeks before the end of pregnancy it drops several inches, causing a change in the figure which is noticeable to the patient, since her skirts hang somewhat lower than before. From this time on she is more comfortable, because the lungs are not crowded, and there is less interference with breathing.
These alterations in the position of the womb indicate very satisfactorily the month to which pregnancy has advanced, but not the week and much less the day. They do not afford a more accurate means of predicting the date of confinement than does quickening. The evidence gained from the position of the womb, like that afforded by the beginning of quickening, generally confirms the prediction made from the menstrual history; it serves only occasionally to correct it.
PROLONGED PREGNANCY.--Since birth does not occur in many cases until the predicted date has been passed, it will be helpful even at the cost of repetition to sum up what we know in explanation of such unfulfilled predictions. They are to be explained sometimes by uncertainty as to the beginning of pregnancy, as for example by the supposition that conception took place shortly after the last menstrual period, whereas it actually occurred two or three weeks later. In a few instances, however, errors of observation or of calculation will not account for false predictions.
It is generally admitted that second pregnancies average somewhat longer than first pregnancies; one series of statistics indicates that the duration increases slightly with each pregnancy up to the ninth and decreases after that. Pregnancy is protracted more frequently in healthy women than in those who are not, and again more frequently in those who are inactive than in those who work. With twins, contrary to the popular belief, pregnancy is apt to end before, not after, the expected date. The sex of the child, in all probability, has no influence upon the duration of pregnancy.
As we might expect, individuality is also a factor in this problem. Thus, the period of gestation with some women is regularly longer, with others habitually shorter than the accepted average. Until experience has demonstrated their existence, generally, such peculiarities are overlooked. But occasionally they may be detected from knowledge of the interval between the menstrual periods; an unusually long interval between them, for example, would lead us to anticipate a protracted pregnancy.
Any delay after the expected date of birth has arrived taxes the patience of the prospective mother. The fact, however, that more than 280 days have passed since the last menstruation, does not necessarily mean that a patient has gone "over time." Such a question can be decided solely from the weight and length of the child. Judged in this way, comprehensive statistics indicate that once in several hundred cases pregnancy may be fairly called prolonged. Even in these rare instances an examination about the time of the predicted date makes it clear whether pregnancy should be artificially ended or be allowed to proceed to its natural conclusion.
THE DEVELOPMENT OF THE OVUM
The Germinal Cells--Fertilization--The First Steps in Development-- The Reaction of the Uterus--The Amniotic Fluid--The Placenta--The Umbilical Cord.
Pregnancy, besides changing the external form of the body, causes sensations--as for example those due to fetal movements--which are so distinctive that they cannot escape notice. These obvious evidences of approaching motherhood naturally lead thoughtful women to wonder about the hidden mechanism of development, a mechanism which, of itself, causes no sensation whatever. It is for this reason, perhaps, that a prospective mother's imagination is so apt to be unusually active, often picturing absurd conditions as responsible for one symptom or another. Those who give free play to the imagination in regard to the formation and progress of the embryo are pretty certain to arrive at erroneous if not grotesque conclusions; for example, they may attribute a protracted pregnancy to the child's having grown fast to the mother, a situation that cannot arise.
Of course it is not essential that a prospective mother should understand what is happening within the womb. And upon those who prefer to be ignorant of the mechanism of development I would not urge another point of view, for not ignorance but the unchallenged acceptance of "half-truths" and of totally incorrect explanations is the chief source of harm. On the other hand, my own experience has taught me that women who wish to know about development should be told the truth. In accord with this is the fact that I never have more satisfactory patients than those who have previously been trained nurses and who, in preparing for that profession, received instruction concerning the reproductive function of human beings.
A description of development, in order to be perfectly clear, must begin with a word about the fundamental structure of the adult body. Everyone knows that the various parts of the body perform different functions; but not everyone, perhaps, realizes that, in spite of their different functions, all the organs of the body are composed of similar structural units, known as cells. Of course, cells are definitely arranged according to the use for which the tissue that they chance to compose may be designed; they have, moreover, distinctive individual peculiarities which can be easily recognized under the microscope; but the essential features of the cells remain the same, wherever they may be located. That is to say, each cell is a minute portion of living matter, or protoplasm, separated from its neighbors by a partition, the cell-membrane; each has its own seat of government, the nucleus, located near its center; and each, to all intents and purposes, leads an individual existence.
THE GERMINAL CELLS.--Many of the cells in the human body are able to produce others of their kind. This they do virtually by growing and splitting in half; cell-division, as this splitting is called, really represents reproduction reduced to the simplest terms. Most cells can do no more than produce units like themselves. The bodies of women contain, however, a type of cell which possesses a far more wonderful
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