From conception the child is a complex, dynamic, rapidly growing organism. By a natural and continuous process the single fertilized ovum will, over approximately nine months, develop into the trillions of cells of the newborn. The natural end of the sperm and ovum is death unless fertilization occurs. At fertilization a new and unique being is created which, although receiving one-half of its chromosomes from each parent, is really unlike either.
About seven to nine days after conception, when there are already several hundred cells of the new individual formed, contact with the uterus is made and implantation begins. Blood cells begin at 17 days and a heart as early as 18 days. This embryonic heart which begins as a simple tube starts regular pulsations at 24 days, which, in about one week, smooth into a rhythmic contraction and expansion.
Straus, et al. have shown that the ECG on a 23 mm embryo (7.5 weeks) presents the existence of a functionally complete cardiac system.... All the classic elements of the adult ECG were seen....
Commencing at 18 days the developmental emphasis is on the nervous system even though other vital organs, such as the heart, are commencing development at the same time. Such early development is necessary since the nervous system integrates the action of all other systems. By the end of the 20th day the foundation of the child's brain, spinal cord and entire nervous system will have been established. By the 6th week after conception this system will have developed so well that it is controlling movements of the baby's muscles, even though the woman may not be aware that she is pregnant. By the 33rd day the cerebral cortex, that part of the central nervous system that governs motor activity as well as intellect may be seen.
The baby's eyes begin to form at 19 days. By the end of the first month the foundation of the brain, spinal cord, nerves and sense organs is completely formed. By 28 days the embryo has the building blocks for 40 pairs of muscles situated from the base of its skull to the lower end of its spinal column. By the end of the first month the child has completed the period of relatively greatest size increase and the greatest physical change of a lifetime. He or she is ten thousand times larger than the fertilized egg and will increase its weight six billion times by birth, having in only the first month gone from the one cell state to millions of cells.
By the beginning of the second month the unborn child, small as it is, looks distinctly human. Yet, by this time the child's mother is not even aware that she is pregnant.
At the end of the first month the child is about 1/4 of an inch in length. At 30 days the primary brain is present and the eyes, ears and nasal organs have started to form. Although the heart is still incomplete, it is beating regularly and pumping blood cells through a closed vascular system. The child and mother do not exchange blood, the child having from a very early point in its development its own and complete vascular system.
Earliest reflexes begin as early as the 42nd day. The male penis begins to form. The child is almost 1/2 inch long and cartilage has begun to develop.
Even at 5 1/2 weeks the fetal heartbeat is essentially similar to that of an adult in general configuration.
By the end of the seventh week we see a well proportioned small scale baby. [Emphasis added.] In its seventh week, it bears the familiar external features and all the internal organs of the adult, even though it is less than an inch long and weighs only 1/30th of an ounce. The body has become nicely rounded, padded with muscles and covered by a thin skin. The arms are only as long as printed exclamation marks, and have hands with fingers and thumbs. The slower growing legs have recognizable knees, ankles and toes.
The new body not only exists, it also functions. The brain in configuration is already like the adult brain and sends out impulses that coordinate the function of the other organs. The brainwaves have been noted at 43 days. The heart beats sturdily. The stomach produces digestive juices. The liver manufactures blood cells and the kidneys begin to function by extracting uric acid from the child's blood. The muscles of the arms and body can already be set in motion.
After the eighth week no further primordia will form; everything is already present that will be found in the full term baby. As one author describes this period: "A human face with eyelids half closed as they are in someone who is about to fall asleep. Hands that soon will begin to grip, feet trying their first gentle kicks."
From this point until adulthood, when full growth is achieved somewhere between 25 and 27 years, the changes in the body will be mainly in dimension and in gradual refinement of the working parts.
The development of the child, while very rapid, is also very specific. The genetic pattern set down in the first day of life instructs the development of a specific anatomy. The ears are formed by seven weeks and are specific, and may resemble a family pattern. The lines in the hands start to be engraved by eight weeks and remain a distinctive feature of the individual.
The primitive skeletal system has completely developed by the end of six weeks. This marks the end of the child's embryonic (from Greek, to swell or teem within) period. From this point, the child will be called a fetus (Latin, young one or offspring).
In the third month, the child becomes very active. By the end of the month he can kick his legs, turn his feet, curl and fan his toes, make a fist, move his thumb, bend his wrist, turn his head, squint, frown, open his mouth, press his lips tightly together. He can swallow and drinks the amniotic fluid that surrounds him. Thumb sucking is first noted at this age. The first respiratory motions move fluid in and out of his lungs with inhaling and exhaling respiratory movements.
The prerequisites for motion are muscles and nerves. In the sixth to seventh weeks, nerves and muscles work together for the first time. If the area of the lips, the first to become sensitive to touch, is gently stroked, the child responds by bending the upper body to one side and making a quick backward motion with his arms. This is called a total pattern response because it involves most of the body, rather than a local part. Localized and more appropriate reactions such as swallowing follow in the third month. By the beginning of the ninth week, the baby moves spontaneously without being touched. Sometimes his whole body swings back and forth for a few moments. By eight and a half weeks the eyelids, and the palms of the hands become sensitive to touch. If the eyelid is stroked, the child squints. On stroking the palm, the fingers close into a small fist.
In the ninth and tenth weeks, the child's activity leaps ahead. Now if the forehead is touched, he may turn his head away and pucker up his brow and frown. He now has full use of his arms and can bend the elbow and wrist independently. In the same week, the entire body becomes sensitive to touch.
The twelfth week brings a whole new range of responses. The baby can now move his thumb in opposition to his fingers. He now swallows regularly. He can pull up his upper lip; the initial step in the development of the sucking reflex. By the end of the twelfth week, the quality of muscular response is altered. It is no longer marionette-like or mechanical - the movements are now graceful and fluid, as they are in the newborn. The child is active and the reflexes are becoming more vigorous. All this is before the mother feels any movement....
Every child shows a distinct individuality in his behavior by the end of the third month. This is because the actual structure of the muscles varies from baby to baby. The alignment of the muscles of the face, for example, follow an inherited pattern.
Further refinements are noted in the third month. The fingernails appear. The child's face becomes much prettier. His eyes, previously far apart, now move closer together. The eyelids close over the eyes. Sexual differentiation is apparent in both internal and external sex organs, and primitive eggs and sperm are formed. The vocal cords are completed. In the absence of air they cannot produce sound; the child cannot cry aloud until birth although he is capable of crying long before.
The taste buds and salivary glands develop in this month, as do the digestive glands in the stomach. When the baby swallows amniotic fluid, its contents are utilized by the child. The child starts to urinate.
From the twelfth to the sixteenth week, the child grows very rapidly. His weight increases six times, and he grows to eight to ten inches in height. For this incredible growth spurt the child needs oxygen and food. This he receives from his mother through the placental attachment - much like he receives food from her after he is born. His dependence does not end with expulsion into the external environment. We now know that the placenta belongs to the baby, not the mother, as was long thought.
In the fifth month, the baby gains two inches in height and ten ounces in weight. By the end of the month he will be about one foot tall and will weigh one pound. Fine baby hair begins to grow on his eyebrows and on his head and a fringe of eyelashes appear. Most of the skeleton hardens. The baby's muscles become much stronger, and as the child becomes larger his mother finally perceives his many activities. The child's mother comes to recognize the movement and can feel the baby's head, arms and legs. She may even perceive a rhythmic jolting movement - fifteen to thirty per minute. This is due to the child hiccoughing .... The doctor can already hear the heartbeat with his stethoscope.
The baby sleeps and wakes just as it will after birth. When he sleeps he invariably settles into his favorite position called his "lie". Each baby has a characteristic lie. When he awakens he moves about freely in the buoyant fluid turning from side to side, and frequently head over heel. Sometimes his head will be up and sometimes It will be down. He may sometimes be aroused from sleep by external vibrations. He may wake up from a loud tap on the tub when his mother is taking a bath. A loud concert or the vibrations of a washing machine may also stir him into activity. The child hears . . . his mother's voice before birth.
In the sixth month, the baby will grow about two more inches, to become fourteen inches tall. He will also begin to accumulate a little fat under his skin and will increase his weight to a pound and three-quarters. This month the permanent teeth buds come in high in the gums behind the milk teeth. Now his closed eyelids will open and close, and his eyes look up, down and sideways. Dr. Liley feels that the child may perceive light through the abdominal wall. Dr. Stiff has noted that electroencephalographic waves have been obtained in forty-three to forty-five day old fetuses, and so conscious experience is possible after this date.
In the sixth month, the child develops a strong muscular grip with his hands. He also starts to breathe regularly and can maintain respiratory response for twenty-four hours if bom prematurely. He may even have a slim chance of surviving in an incubator. The youngest children known to survive were between twenty to twenty-five weeks old.