Читать книгу Obstetrical Nursing - Carolyn Conant Van Blarcom - Страница 14

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As we learned in the last chapter, some of the ova which are discharged into the peritoneal cavity enter the fimbriated end of the tube, while very many others perish. As a rule an ovum enters the tubal opening adjacent to the ovary from which it has been discharged, but it is possible for this tiny cell to travel across the body and enter the tube on the opposite side.

This migration of the ovum, as it is termed, has been demonstrated in cases in which pregnancy has followed removal of the ovary on one side and the tube on the other.

Fig. 17.—Diagram of spermatozoa, the male cells of germination.

There are various theories as to how and why an occasional migrating ovum, floating around in a relatively large cavity, ever enters the tubal opening, which, after all, is not large. The most widely accepted belief is that the motion of the cilia lining the tubes creates a suction which draws the microscopical cell into the opening, the same cilia being the means by which the ovum is later propelled downward through the tube to the uterus.

This journey of the ovum through the tube is of enormous consequence. During its course occur the events which decide whether the ovum shall, like most of its fellows, be simply swept along to no end and lost, or whether by chance it is to receive the mysterious impulse which begins the development of a new human being.

The amazing power which enables this cell to reproduce itself, and to develop with unbelievable complexity, is acquired somewhere in the tube by meeting and fusing with a spermatozoon, the germinal cell of the male. (Fig. 17.)

The spermatozoa look very much like microscopic tadpoles, with their flat, oval heads, tapering bodies and long tails. As these tails serve somewhat as propellers, the male cells are capable of very rapid motion. But in spite of their strange appearance, they are cells after all, and resemble the female cells in that each one contains a nucleus, or germinal spot.

An almost inconceivably large number of spermatozoa, floating in the seminal fluid, is deposited in the vagina at the time of intercourse. Nature evidently supplies the male and female cells with equal lavishness, in order to provide for the large number of both kinds which must inevitably be lost, and still have enough survive to accomplish the high purpose of their creation. A very considerable number of spermatozoa enter the uterus, and are enabled through their powers of motility, to travel up into the tubes, in spite of the downward current created by the cilia. And in the tube, usually in the upper end, they meet a recently matured and discharged ovum which is being swept downward, and are attracted to it somewhat as bits of metal are drawn to a magnet. Although the ovum which is destined to be fertilized is surrounded by several spermatozoa, only one actually enters and fuses with it.

This fusion is termed impregnation, fertilization, or, in lay parlance, conception, and the instant at which it occurs marks the beginning of pregnancy. The establishment of this fact is of no little importance, since it does away with any possible controversy concerning the time at which a new life begins. The origin of the child is exactly coincident with the fusion of the male and female germinal cells.

And furthermore, the sex of the child and any inherited traits and characteristics are also established at this decisive instant. No amount of dieting, exercise nor mental effort on the part of the expectant mother can alter or influence them in the smallest degree, for the father has made his complete contribution toward the creation of the new being, and after this event the mother provides nourishment only.

All told, probably more than five hundred theories have been advanced to explain what it is that decides of which sex the forthcoming child will be.

In 1907 Dr. Schenck attracted world wide attention by announcing his belief that either sex could be produced in the expected child through the simple expedient of regulating the mother’s diet. Liberal feeding would result in boys, the sturdier sex, and frugality in girls, the smaller, frailer type of baby. But as the results of applying Schenck’s theory have scarcely borne out his claims, it is given but scant attention to-day.

The present belief regarding the causation of sex is that although there is but one kind of ovum, there are two kinds of spermatozoa, one capable of producing a male, and the other a female child. These two kinds are evidently deposited in the vagina in about equal numbers, and the sex-determining form that fertilizes any one ovum is a matter of the merest chance. Statistics show, however, that more male than female babies are born, the usual proportion being about 105 boys to 100 girls among those that reach full term. Among abortions and premature births there is also a larger number of boys than girls, and in elderly primiparæ the ratio increases to about 130 boys to 100 girls. But as more boys die in infancy than girls, the two sexes about even up in the number of those living to adult age.

Apparently, then, there is some factor operating slightly in favor of the purposeful activities of the male-producing spermatozoa. But so far no accurate means has ever been found whereby it was possible to influence the development or discover the sex of a child before its birth.

There is a wide difference of opinion concerning the time of the month when fertilization is most likely to occur. Observations made upon the wives of sailors and under a variety of conditions suggest that the most favorable period is just before or just after menstruation which represents the second stage of the menstrual cycle.

Dr. Williams believes, however, that fertilization is most likely to occur about midway during the intermenstrual period. But since it is probable that spermatozoa are constantly present in the tubes of women who are exposed to the possibility of becoming pregnant, it is difficult to do more than speculate about the time of the month at which fertility is greatest.

Another moot question relates to the age of the woman at which it is most desirable that the first child shall be born. Recent observations made by Dr. John W. Harris upon a large number of pregnancies occurring in very young girls indicates that from a standpoint which considers solely the physical welfare of the mother and her infant, sixteen years is the most satisfactory age at which to bear the first child.

However, when motherhood is considered from all standpoints, social, ethical, spiritual as well as physical, the consensus of opinion seems to be that the twenty-third year is the most favorable age for motherhood to begin. Children have been born to little girls nine years old and to women of sixty-two, but the extremes of the reproductive years are not favorable periods for child-bearing.

As soon as a spermatozoon enters an ovum, it disappears and is completely absorbed, and, as the ovum in turn is instantly possessed of new powers, the result of this union is a cell which was previously non-existent.

This new cell is not only capable of reproduction by means of segmentation or cell division, but in the course of its sub-division and proliferation, it forms groups of cells which develop into tissues and structures widely different from each other. The entire complex human body, in addition to the placenta, cord, and membranes, arises from the single, extraordinary cell.

It first divides into two; these two divide into four; the four into eight and thus the process of division and sub-division continues until a solid mass is formed, shaped something like a mulberry and called the morula. (Fig. 18.)

While these developmental changes are taking place, the morula is being carried down the tube toward the uterus, by the sweeping motion of the ciliated membrane. The time consumed by this journey has not been definitely ascertained and though possibly it may be made in a few hours, it probably takes from five days to a week. Since the embryo is constantly moving during this time, it quite evidently has no attachment to the mother and cannot, therefore, derive any great amount of nourishment directly from her. The growth and development to this point, then, must be due chiefly to inherent powers within the mass of cells itself.

In all probability, the embryo is still in the morula stage and is about the size of the head of a pin when it reaches the uterus, where it finds that the endometrium has been prepared for its reception by the premenstrual swelling. The mucosa has grown thicker, more velvety and vascular, and its glands have increased in number and activity. The columnar epithelium of the endometrium is replaced by a thick layer of large, vacuolated cells, called decidual cells, and the uterine lining from now on is termed the decidua gravidatis. While the normal uterine mucosa is thin, averaging from 1 to 3 millimetres (0.039 to 0.117 inch) in thickness, it increases to a thickness of about 1 centimetre (⅞ inch) during pregnancy.

Fig. 18.—Diagram of segmenting rabbit’s ovum.

The point at which the embryo attaches itself to this spongy membrane is entirely a matter of chance. It usually rests somewhere in the upper part of the uterine cavity, promptly destroys the minute underlying area of tissue by digestive action and burrows into the decidua. As the margins of the opening thus made meet and fuse above the ovum, it is completely incapsulated in a cavity of its own that has no connection with the uterine cavity. (Fig. 19.)

After this occurrence the decidua consists of three portions: the hypertrophied membrane which lines the uterus as a whole, called the decidua vera, which atrophies during the latter part of pregnancy and is also thrown off in part with the membranes during labor, and later in the uterine discharges; the decidua basalis, or the decidua serotina, is that portion lying directly beneath the embryo which later enters into the formation of the placenta; and the decidua reflexa, which surrounds and covers the buried embryo, consists of the developed and fused margins of the pit in the mucosa, that have grown over the embryo.

Fig. 19.—Ovum about 13 days old, embedded in the decidua. (The Bryce-Teacher ovum from Human Embryology by Keibel and Mall.)

As the cellular activity continues within the morula, fluid appears in the centre with the result that the cells are rearranged and pushed toward the periphery, thus forming a sac. At this stage the embryo is called the blastodermic vesicle.

At one point on the inner surface of this vesicle the cells proliferate and form a mass which is sometimes called the internal cell mass, or embryonic area, and the single layer of cells comprising the remainder of the vesicular wall, the primitive chorion. The cells in the mass are at first disposed in layers, the outer layer being termed the ectoderm; the inner layer the entoderm, while a third layer which appears a little later is called the mesoderm.

Although these three primitive layers of cells have all arisen from the single cell formed by the fused spermatozoon and ovum, they are even now very different in character. The differences steadily increase until finally all of the complex fetal organs and tissues, the membranes, cord and placenta, result from their further specialization and development, as follows:

From the ectoderm arises the skin with its appendages, and the salivary and mammary glands; the nasal passages, upper part of the pharynx and the anus; the crystalline lens, the external ear, the entire nervous system, the sense organs and, in part, the fetal membranes.

From the mesoderm are derived the urinary and reproductive organs; the muscles, bones, and connective tissues and the circulatory systems.

From the entoderm are developed the alimentary canal, the thymus, thyroid, liver, lungs, pancreas, bladder and the various small glands and tubules.

It was formerly believed that the human being existed in miniature in the first cell and that its development during pregnancy was entirely a matter of increase in size. But the microscope has disproved this, and we now know that embryonic development comprises both growth and evolution.

Much of the information accepted to-day is, of course, speculative, having been deduced from observations made upon the reproductive processes of lower mammals, since the youngest human ovum which has been discovered and examined was probably two weeks old. But the evidence points quite convincingly to the belief that the early stages of development consist of proliferation of and alterations in the kinds of cells, their arrangement into groups, and a differentiation of the functional activity of these groups of cells before the mass assumes human form and develops organs.

As to terminology, some authorities call this mass the embryo during this stage of grouping and differentiation, which corresponds to the first six weeks of pregnancy, and the fetus from then until the time of delivery. By others it is designated the ovum during the first two weeks of pregnancy, the embryo from the third to the fifth week, after which it is known as the fetus.

From the nurse’s standpoint these distinctions are of no consequence, for the mass may safely be called a fetus from the time that the expectant mother looks to the nurse for guidance and care.

It is scarcely warrantable to take the time and space which would be necessary to trace in detail through its various stages the intricate development of the human body, with its attached membranes. But the whole question is so important and so interesting that we shall at least have a word of description as to its size and characteristics at successive periods.

Although the exact length of time required for the maturation of the fetus is not known, it is estimated that two hundred and eighty days, or ten lunar months, elapse between the beginning of the last menstrual period and the beginning of labor. And in spite of the difference in size among the mothers, it is found that the products of conception develop and grow at a fairly uniform rate of speed.

A new human being is the ultimate result of conception, but the chorion, amnion, placenta and umbilical cord must also be created to serve as aids in building and protecting the developing child during its uterine life. The part played by these accessory structures is so vital, in spite of being temporary, that it will be well for us to look into their origin and functions before considering the fetus itself which they serve.

The Chorion and Placenta. Very early in pregnancy, probably while the fertilized ovum is journeying down the tube, tiny, thread-like projections, called villi, appear over the surface of the primitive chorion, giving it the shaggy appearance of a chestnut burr. Shortly after this shaggy ovum reaches the uterus and is embedded in the lining, the chorion, or the outer fetal membrane, is formed, being partly derived from the ectodermal layer of cells growing within the blastodermal vesicle. The chorion grows rapidly in size and thickness, and the villi upon its surface increase in size, number and complexity by frequent branching. In so doing the villi push their way into the maternal tissues surrounding them, and destroy the capillary walls with which they come in contact. Maternal blood escapes through the destroyed walls, forming tiny hemorrhagic areas, or “lakes of blood.” The chorionic villi float freely in these pools of maternal blood, which is constantly being refreshed by an inflow of arterial and an outflow of venous blood through the mother’s vessels.

Blood vessels soon appear in these chorionic villi, and fetal blood then circulates through them. It becomes apparent, therefore, that the maternal and fetal blood streams are in such close relation that they are separated by only the thin membrane which forms the walls of the vessels in the villi. (Fig. 20.)

Fig. 20.—Diagram of fetus, cord, membranes and placenta in utero at an early stage of their development.

This arrangement makes it possible for the steadily proliferating villi to discharge one of their functions, which is to receive from the maternal blood nourishment for the embryo, and give up to the parent waste products from the growing body. This exchange of nourishment and waste matter takes place by means of osmosis. But freely as the exchange of materials occurs, there is never any contact, or mixing of maternal and fetal blood, nor does maternal blood at any time flow through fetal vessels. It was believed at one time that the fetus was nourished by milk which was in some way secreted by the gravid uterus, but this is disproved by present knowledge of the placental function.

The second function of the villi, particularly after they have developed to the placental stage, is to assist in securely attaching the embryo to the uterine wall.

The villi are equally distributed over the surface of the chorion at first, but as the sac increases in size and pushes out into the uterine cavity, they gradually atrophy and disappear, excepting over the small area beneath the vesicle where the chorion is in contact with the decidua basalis. At this site the villi become much more abundant, and it is here that the placenta eventually develops. This part of the chorion is termed the chorion frondosum, while the remainder, which is in contact with the decidua capsularis, is the chorion læve.

As pregnancy advances and the fetal sac enlarges, the chorion læve covered by the decidua capsularis, or reflexa, is pushed farther out into the uterine cavity, until finally it quite reaches the opposite wall, meets the decidua vera and obliterates the entire space which had existed between the two membranes. This means that instead of a uterine cavity lined with decidua, and a tiny capsule somewhere off to the side lined with chorion, the latter has distended until it completely fills and really becomes the cavity within the uterine walls, thus lining the uterus with chorion and crowding the original lining out of existence. The decidudae capsularis and vera fuse in time and finally the capsularis degenerates and disappears.

The Amnion. Returning for a moment to the blastodermal stage of the ovum, we find that the amnion, or inner membrane, first appears as a tiny vesicle over the dorsal surface of the embryo. Very soon, however, it invests the embryo completely, and the membranous sac is intact, excepting where it is pierced by the umbilical cord. The amnion, too, is derived in part from the ectoderm, but is a stronger, denser membrane than the chorion. At first there is an appreciable space, and some fluid, between the two membranes, but as the amnion increases in size with the advance of pregnancy, it comes in contact with and is loosely adherent to the chorion.

Very early in its development the amniotic sac contains a pale yellow fluid known as the amniotic fluid, or liquor amnii, in which the fetus floats. This fluid increases in amount until the end of pregnancy and though the quantity is variable, it usually amounts to about a quart.

The source of the liquor amnii is not definitely known, but it is generally believed to be of maternal origin, secreted from the amniotic membrane, though the possibility of its consisting partly of fetal urine cannot be overlooked. It is about 99% water, containing particles of dead skin and lanugo, a soft downy hair cast off from the body of the fetus, traces of albumen and both organic and inorganic salts.

Fig. 21.—Diagram showing general structure and relation of membranes, placenta and cord.

The amniotic fluid serves a variety of purposes. Since the intestines of the fetus contain lanugo and particles of dead skin, it is evident that the child swallows some of this fluid during its uterine life, and possibly obtains in this way much of the fluid necessary for its development.

The increasing bulk of the fluid serves to distend the fetal sac and surrounding uterus, and thus provides the fetus with room for growth and movement. It also prevents adhesions between the child’s skin and the amnion, which are a factor, when by mischance they do occur, in causing monstrosities and intrauterine amputations. The fluid with which it is surrounded keeps the fetus at an equable temperature in spite of variations of temperature in the mother’s environment, and minimizes the danger of injury to the fragile little body, from pressure or blows on the mother’s abdomen. And by acting as a water wedge, forced down by uterine contractions at the time of labor, it dilates the cervix sufficiently to permit the expulsion of the full term child.

Fig. 22.—Placental blood vessels. Note their branching, tree-like arrangement. (Photographed from an injected specimen in the Obstetrical Laboratory, Johns Hopkins Hospital.)

The placenta. The placenta, in lay parlance the after-birth, is really a thickened, amplified portion of the fetal sac, which has developed at the site of the implantation of the ovum. It is partly fetal and partly maternal in origin, being developed jointly from the chorion frondosum with its branching villi, and the underlying decidua basalis.

The chorionic villi already referred to grow and branch in a tree-like fashion (Fig. 22), and push their way farther and farther into the uterine tissues creating the intervillous spaces which fill with maternal blood. From the time that the first fetal blood vessels appear in these floating villi, until the child is born, there is a constant exchange of nutriment and waste matter between the maternal and fetal blood; the arterial maternal blood in the intervillous spaces giving to the fetal blood in the villi the oxygen and other substances necessary to nourish and build the growing young body, and receiving in return the broken-down products of fetal activity. The waste is carried by the maternal blood stream to the mother’s lungs, kidneys and skin, by which it is excreted.

This exchange of substances is accomplished by osmosis and also by selective powers of the cells in the villi. Thus the placenta virtually serves the fetus as lungs, stomach, intestines and kidneys throughout its uterine life.

In addition to the nutritive substances in the mother’s blood, such as albumen, iron and fat which are so altered by cell action as to be absorbable through the villi, certain protective substances as the anti-toxines of diphtheria, tetanus, colon and typhoid bacilli are evidently transmitted from the maternal to the fetal circulation. It is claimed by some authorities that pathogenic organisms, for example, anthrax, pneumonia and tubercle bacilli, may be transmitted from mother to fetus, but the reported cases are so rare that the accepted belief is that organisms are seldom transmitted, if the placenta is healthy and intact. But, according to Dr. Williams, the transmission of typhoid occurs frequently, though malarial parasites cannot pass through the villous membranes.

Only during comparatively recent years has accurate knowledge of the origin and function of the placenta been available. Many varied and interesting beliefs and superstitions gained currency in the past, but all of them were erroneous.

The description of the circulation of the blood by William Harvey in 1628 shed considerable light upon this puzzling question concerning the exchange of fuel and ash between the parent and fetal bodies. But a mistaken belief that the maternal blood actually entered and flowed through the fetal vessels resulted from his valuable discovery.

Fig. 23.—Maternal surface of the placenta, surrounded by the membranes and cord. (From a photograph taken at Johns Hopkins Hospital.)

When we examine this interesting structure, the placenta, after it is cast off, we find it to be a flattened, fairly round, spongy mass, eight or nine inches in diameter, about an inch thick where the cord arises and thinning out toward the margin. Continued from the margin are the filmy fetal membranes, which together form a ruptured sac. The rupture in these membranes is the opening through which the amniotic fluid escapes, and the child passes during birth.

Fig. 24.—Fetal surface of the placenta showing origin of cord. (From photograph taken at Johns Hopkins Hospital.)

The placenta weighs about a pound and a quarter, or ⅙ as much as the child, and accordingly varies in size and weight with the baby. The maternal surface (Fig. 23) having been detached from the uterine wall, is rough and bleeding and is irregularly divided into lobes while the inner, or fetal, surface is smooth and glistening and covered with the amnion. The fetal surface (Fig. 24) is traversed by a number of large blood-vessels which converge toward the point of insertion of the umbilical cord, from the vessels of which they really arise. These vessels branch and divide until their termination in the innumerable chorionic villi floating in the lakes of maternal blood.

The Umbilical Cord. The cord, or funis, is a bluish white cord about three-quarters of an inch in diameter, twisted and tortuous throughout its length of about twenty inches. It is the one actual link between the mother and her unborn child, one end being attached to the abdomen of the fetus, about midway between the ensiform and the pubis, and the other to the inner surface of the placenta. The cord is derived from the abdominal pedicle and is merely an extension of the caudal or tail end of the embryo. It is covered with a layer of ectoderm which is continuous with the ectodermal covering of the fetus.

The cord consists of a gelatinous mass known as Wharton’s jelly, in the centre of which are embedded three blood vessels; two arteries through which the vitiated blood flows to the placenta, where it gives up its ash; and one vein which carries oxygenated, nourishment-bearing blood back to the fetus. The life of the fetus, therefore, is absolutely contingent upon an uninterrupted, two-way flow of blood through the cord.

The Fetus. In tracing the development of the ovum after its implantation in the uterine lining, we begin, as previously stated, with a shaggy-looking vesicle, containing fluid, with a clump of cells hanging toward the centre from their point of attachment on the inner surface of the sac. This clump develops into the embryo.

During the first month the mass increases in size, becomes somewhat elongated and curved upon itself with the two extremities almost in contact. The abdominal pedicle, which later becomes the umbilical cord, appears; the alimentary canal exists as a straight tube and the thymus, thyroid, lungs and liver are recognizable. The heart, eyes, nose, ears, and brain appear in rudimentary form and the extremities begin to be evident as tiny, bud-like projections on the surface of the embryo.

By the end of the fourth week the sac is about the size of a pigeon’s egg and has two walls. The outer wall, or chorion, as we have already seen, is covered with villi, and the amnion, or inner wall, is smooth; the contained embryo is surrounded by amniotic fluid and measures about 10 millimetres or 4 inches in length.

Fig. 25.—Embryo, about 5.5 centimetres long in amniotic sac; uterine wall incised, chorion split and turned back. Drawn by Max Brodel. (From The Umbilicus and Its Diseases, by Thomas R. Cullen, M.D.)

By the end of the second month, or eighth week, the head end of the embryo has greatly increased in size and is about as large as the rest of the body. Bone centres appear in the rudimentary clavicles; the kidneys and supra-renal bodies are formed; the limbs are more developed, webbed hands and feet are formed, the external genitalia are apparent but the sex is not distinguishable. The amnion is distended with fluid, but it is not yet in contact with the chorion; the chorionic villi have become more luxuriant on that part of the chorion resting on the decidua basalis, the future site of the placenta. The approximate weight of the embryo is 4 grams and its length 25 millimetres or an inch.

By the end of the third month, or twelfth week, centres of ossification have appeared in most of the bones, the fingers and toes are separated and bear nails in the form of fine membranes; the umbilical cord has definite form, has increased in length and begun to twist. The neck is longer, teeth are forming and the eyes have lids. The amnion and chorion are now in contact, and the villi have disappeared excepting at one point where a small, but complete placenta has developed. The embryo is about 9 centimetres long and weighs about 30 grams.

Fig. 26.—Diagram showing appearance of fetus at different stages in its development.

By the end of the fourth month, or sixteenth week, all parts show growth and development; lanugo appears over the body; the sex organs are clearly distinguishable and there is tarry fæcal matter, called meconium, in the intestines. The placenta is larger, the cord longer, more spiral and also thicker because of the Whartonian jelly which is beginning to form. The fetus is about 15 centimetres long and weighs about 120 grams.

By the end of the fifth month, or twentieth week, the fetus has both grown and developed markedly. It is now covered with skin on which are occasional patches of vernix caseosa, a greasy, cheesy substance consisting largely of a secretion of the sebaceous glands. There is some fat beneath the skin but the face looks old and wrinkled. Hair has appeared upon the head and the eyelids are opening. It is usually during the fifth month that the expectant mother first feels the fetal movements which are commonly referred to as “quickening.” The body is about 25 centimetres long and weighs about 280 grams.

By the end of the sixth month, or twenty-eighth week, the fetus still looks thin and scrawny, the skin is reddish and is well covered with vernix caseosa and the intestines contain an increased amount of meconium. If born at this time the child will move quite vigorously and cry feebly. Although it is not likely to live for any length of time, every effort should be made to save its life, for it may be that the high rate of mortality at this age is due to the inadequacy of the attempts which are usually made to save the child rather than to the frailty of the child itself. It is about 35 centimetres long and weighs about 1200 grams.

By the end of the eighth month, or thirty-second week, the child has grown to about 42 centimetres in length and 1900 grams in weight, but continues to look thin and old and wrinkled. The nails do not extend beyond the ends of the fingers but are firmer in texture; the lanugo begins to disappear from the face but the hair on the head is more abundant. If born at this stage, the baby will have a fair chance to live, if given painstaking care. This is true in spite of the ancient superstition, still widely current, that a seven months’ baby is more viable than one born at eight months (meaning calendar months). The fact is that after the eighth lunar month, a little more than seven calendar months, the probability of the child’s living increases rapidly with the length of its intra-uterine life.

By the end of the ninth month, or thirty-sixth week, the increased deposit of fat under the skin has given a plumper, rounder contour to the entire body; the aged look has passed and the chances for life have greatly increased. The baby now weighs about 2500 grams and is about 46 centimetres long.

The end of the tenth month, or fortieth week, usually marks the end of pregnancy. (Fig. 27.) The average, normally developed baby has attained a length of 50 centimetres (20 inches), and a weight of 3250 grams, or about 7¼ pounds, boys usually being about three ounces heavier than girls.

It must be remembered, however, that these figures merely represent the average drawn from a large number of cases, for there may be a variation in weight among entirely normal healthy babies from a minimum of 2300 grams (5 pounds) to as high as 5000 grams (11 pounds), or more. Babies actually weighing more than 12 pounds are seldom born, in spite of legends and rumors to the contrary.

The length of a normal baby is less variable than the weight. In fact, it is so nearly constant in its increase during the successive months of pregnancy, that the age of a prematurely born fetus may be fairly accurately estimated from its length. This fact is of no little practical importance, since it aids the obstetrician in making a prognosis as to the child’s prospect of living, for he can estimate its intra-uterine age from its body length.

The size of the baby is affected by race, colored babies, for example, averaging a smaller weight than white babies. And, as might be expected, the size of the parents is likely to be reflected in the size of their infants, large parents tending to have large children and vice versa.

The number of children which the mother has previously borne is also a factor, since the first child is usually the smallest, the size of those following showing an increase with the mother’s age up to her twenty-eighth or thirtieth year, provided the successive pregnancies do not occur at too frequent intervals.

The expectant mother’s general state of health, her state of nutrition, the character of her surroundings and her mode of living may be expected to influence her baby’s welfare. Hence, women who live in comfortable, or luxurious circumstances usually have more robust babies than those who are run down, poorly nourished or overworked. All of which hints at the great value of prenatal care which will be taken up in detail in a later chapter.

Fig. 27.—Full term fetus in utero. Drawn by Max Brodel. (Used by permission of A. J. Nystrom & Co., Chicago.)

A multiple pregnancy is one in which the pregnant uterus contains two or more embryos, these being termed twins when there are two and triplets when there are three; quadruplets, quintuplets and sextuplets when there are four, five and six embryos, respectively, six being the largest accredited number on record.

The tendency to multiple pregnancies is apparently inherited, and it sometimes happens that several members of the same family connection have this predisposition, as evidenced by the number of twins and triplets to be found among relatives. It is estimated that twins occur once in 90 pregnancies and triplets once in about 7000 cases.

Twin pregnancies may result from the fertilization of one or of two ova, and are designated as single ovum or double ovum twins respectively. In single ovum twins the egg becomes divided early in its development and two embryos are formed. In such a case there is one placenta, one chorion and two amnions and the babies are of the same sex.

In double ovum twins two ova are fertilized; both may come from the same ovary or there may be one from each side. When double ovum twins occur, there are two placentæ, as a rule, though they may be somewhat fused; two amnions and two chorions and the babies may be of the same sex or each of a different sex.

Twins are often prematurely born and each one is likely to be smaller than a baby resulting from a single pregnancy, but their combined weight is greater than that of one normal baby.

An extra-uterine pregnancy may be defined as a pregnancy which develops outside of the uterus, usually in a tube or ovary. Although in the normal course of events the fertilized ovum travels down the tube and becomes attached to the uterine lining, it is possible for it to stop, and more or less completely develop at any point along the way between the Graafian follicle, from which it has been projected, and the uterus toward which it is traveling. If the fetus develops in the ovary, it is termed an ovarian pregnancy, and a tubal pregnancy if it occurs in the tube, the latter being the most frequent variety of extra-uterine pregnancy.

In the opinion of Dr. Mall, only about 1 per cent of all extrauterine pregnancies are capable of going to term. There may be an abortion, when the fetus and membranes are partly or completely extruded from the fimbriated end of the tube into the peritoneal cavity; or a rupture of the tube, when the fetus, with or without the membranes, may be expelled into the peritoneal cavity, or between the folds of the broad ligament. If the greater part of the placenta remains attached to the site of its development, in the case of a ruptured tube, it is possible for the fetus to live and grow and even go to term. But if the placenta is nearly, or completely separated, the fetus perishes and may be largely absorbed by the maternal organism, or mummified, or putrefactive changes may take place. It is usually customary to terminate an extra-uterine pregnancy as soon as it is diagnosed, for only a very small number can be expected to go to term, the majority aborting, or rupturing the tube, with serious hemorrhage from the mother as a frequent result.

To sum up the normal pregnancy, we find that in the course of ten lunar months, following the fertilization of an ovum, the uterus grows from a small, flattened, pelvic organ, three inches in length, to a large, globular, muscular sac, constituting an abdominal tumor about fifteen inches long; it increases its weight thirty-two times, that is from two ounces to two pounds, while the capacity of the uterine cavity is multiplied five hundred times. Within the cavity is a child weighing about seven and a quarter pounds, surrounded by a quart or so of amniotic fluid. This fluid is contained in the sac composed of the fetal membranes, the amnion and chorion, which are excessively developed at one point into the placenta. The placenta, in turn, is attached to the child by means of the umbilical cord. The total weight of the uterus and its contents at term is usually about fifteen pounds.

Quite as mysterious and inexplicable as the development of these complex structures from one tiny cell is the fact that when the new human being is ready to begin life as a separate entity, further changes occur within the mother’s body which produce uterine contractions of such a character as to entirely empty the uterus of its contents.