The Prospective Mother, a Handbook for Women During Pregnancy

by J. Morris Slemons

The amniotic fluid performs many important duties. Perhaps the first, in point of time, is to provide sufficient room for the embryo to grow in. Later, as the fluid increases, it permits the fetus to move freely, and yet renders the movements less noticeable to the mother. Again, the amniotic fluid prevents injuries that might otherwise befall the child in case the mother wears her clothing too tight. Harmful as the practice of tight-lacing during pregnancy is, it does not, thanks to the presence of the amniotic fluid, result in the disfigurement of the child. For the same reason a blow struck upon the abdomen, as in a fall forward, is not so serious as might be thought, since the fluid, not the child, receives the force of the impact. Some physicians believe that the fetus swallows the amniotic fluid and thus secures nourishment. The fluid also serves to keep the fetus warm; or, to be more exact, protects it from sudden changes in the temperature of the mother's environment. Normally the temperature of the fetus is thus kept nearly one degree higher than the temperature of the parent.

Ultimately, the amniotic fluid assists in dilating the mouth of the womb, which remains closed until the beginning of the process that terminates with birth. The uterine contractions at the onset of labor compress the fluid; in turn the fluid attempts to escape but is held in check by the amniotic membrane, which it drives into the canal leading from the uterine cavity to the vagina. Acting like a wedge, the fluid gradually pushes the mouth of the womb wider and wider open, until it is large enough for the child to pass. The sac usually ruptures when that point is reached, the fluid escapes, and in due time the child is born. This is followed within half an hour by the extrusion of a mass of tissue—in reality the collapsed fetal sac— which in every language, so far as I know, is named the After-Birth. An examination of this tissue at the time of delivery repays the physician, for it is important to ascertain that none of it has been left in the uterus. Our interest at present, however, is to learn how the after-birth has assisted toward the growth of the child.

THE PLACENTA.—The after-birth has puzzled scientists as well as the laity, and not until comparatively recent times have its origin, structure, and use been satisfactorily explained. Its meaning profoundly interested primitive men and stimulated their imagination scarcely less than the mystery of conception. Some uncivilized tribes believed that the after-birth was animated like the child; consequently they spoke of it as "the other half," and often saved it to give to the child in case of sickness. But generally the after- birth was buried with religious ceremony, and was occasionally unearthed later to discover whether the woman would have other children; the prophecy was made according to the manner of disintegration or some other equally absurd circumstance.

The after-birth consists of a round, fleshy cake, the placenta, to which two very essential structures are attached. One of these, running from one surface of the cake, is a rope-like appendage, the umbilical cord, which links the placenta with the fetus. The other, attached to the circular edge of the cake, is a thin veil of tissue, in some part of which a rent will be found. Now, if we lift the margin of the rent, we shall see that the veil and the cake together form a sac which we are holding by the opening. This aperture through which the fetus passed, and it was really made for that purpose, was formerly placed over the mouth of the womb; the sac itself, distended by the fetus and the amniotic fluid, was fastened everywhere to the inner surface of the womb.

It is plain that we have now in our hands the fetal sac, the development of which we have already traced from the beginning. The wall of the sac, it will be recalled, was originally of the same formation throughout; but when the ovum became imbedded in the womb, that part of its capsule which remained in permanent contact with the mother's blood underwent special development, whereas the rest of the capsule gradually pushed away from its primary position and, becoming stunted in its growth, even lost to some degree the development it had attained. This latter portion, the veil that passes from the edge of the placenta, is formed of the two membranes we have mentioned, namely, the chorion and the amnion.

The placenta is, for the most part, a highly developed portion of the chorionic membrane, which became specialized simply because it happened to receive the best supply of blood. At the time of birth the placenta measures nearly an inch in thickness, is as large around as a breakfast-plate, and generally weighs a pound and a quarter, that is, approximately one-sixth of the weight of the child. This relation between the weight of the placenta and of the child is regularly maintained; therefore, the larger the child the larger the placenta associated with it.

The placenta has two surfaces, easily distinguished from each other. The raw maternal surface was formerly attached to the inside of the uterus; the fetal surface, covered by the amniotic membrane, was in contact with the amniotic fluid. Across the fetal surface run a number of blood-vessels containing the child's blood, converging toward a central point at which the umbilical cord is inserted. The point at which the cord is attached affords the simplest means of distinguishing the two surfaces of the placenta.

Our knowledge as to how the exchange of food and excretory products between mother and child is carried on by the placenta has been gained chiefly through the microscope. The oldest medical writings, as we might suppose, express very fanciful ideas regarding the nature of embryonic development and the means by which it is made possible; no rational view of these matters could exist until the circulation of the blood was described by William Harvey in 1628. After this epoch-making revelation, it was accepted as true that the mother's blood entered the unborn child and returned to her own system. But that view eventually became untenable, for it was proved conclusively that there is no communicating channel between the two. For years after that, it was believed that before birth the womb manufactured milk to sustain the child, just as the breasts do afterwards; but this theory also was disproved; and, as I have said, only by the use of the microscope have we learned the truth about fetal nutrition.

When thin slices of the placenta are magnified they are found to contain countless numbers of tiny, finger-like processes; these are the villi, and they constitute the major portion of the organ. The villi seen in a mature placenta are the same as those which projected from the capsule of the young ovum, but not these alone, for many branches have sprouted from the original projections. The primary trunks with all their branches hang from the capsule of the ovum and extract nutriment from the mother's blood which surrounds them, just as the roots of a tree extract it from the soil.

The interchange of material between mother and child as carried on in the placenta can, perhaps, be made clearer if we compare one of the trunks and its branching villi to a human forearm, hand, and fingers. The hand, we will imagine, is held in a basin of water, in which, by turning on a spigot and leaving the outflow unstopped, we have arranged that the water changes constantly. In terms of this illustration, the water corresponds to the mother's blood, rich in oxygen, mineral matter, and all other kinds of essential nutriment; and the fingers are the villi. The blood-vessels in the fingers, to go a step farther, represent the blood-vessels which exist within the villi, connecting with the umbilical cord, and passing by that route to the body of the child. The blood which thus circulates through the villi, it is important to emphasize, is the child's blood; it cannot escape through the coating of the villi, just as our blood cannot escape through the skin of the fingers. Similarly, the mother's blood cannot enter the child; the two circulations are absolutely separate and distinct.