Once the embryo, with its fluid sac surrounding it, is buried in the wall of the uterus, it develops quickly. It grows from the size of a pinhead at one week of age to that of a pea at five weeks of age, to that of a limb bean at eight weeks of age, and to that of a hen’s egg by the time it is two and a half months along the road to development. Of course, as it grows during the first few weeks, the embryo doesn’t look much like a baby because it hasn’t really begun to take shape. However, even at six weeks, the primitive tissues that will eventually form the eyes, ears, arms, legs, head, chest, abdomen, spine and other organs can be seen. If the embryo were to be examined at this time, these parts could actually be recognized under a magnifying glass.
At first the embryo doesn’t look much like a human being, and it passes through many stages of development that resemble various forms of animal life. In the early days of the first few weeks, the embryo resembles a fish, then a frog, and finally takes on the shape of an animal with four limbs. But it grows and changes so quickly that by the end of three months in its mother’s uterus, it really looks like a human baby. Its head, neck, chest, abdomen, arms, legs, fingers, toes, and even nails begin to appear as they will when the infant is born.
The developing baby is called a fetus when it reaches the age of about three to three and a half months. At about four and a half months after pregnancy has begun, the mother starts to feel the baby moving around within her uterus. We say the mother “feels life,” and we know that the fetus is growing actively.
The unborn child is attached to its mother by a cordlike structure that extends from its abdomen to the placenta. The structure is called the umbilical cord. The placenta is a large, round, flat structure almost as large as a dinner plate that attaches to the wall of the uterus. The nourishment and oxygen so necessary to life pass from the mother’s blood into the blood vessels of the placenta. This nourishment, containing all the proteins, necessary sugars, fats, vitamins, minerals, and fluids, then flows through the placenta into the blood vessels of the umbilical cord. From there, it enters the baby’s body in the abdominal region and travels throughout the blood vessels of the baby. The waste products resulting from use of the nourishing substances flows out. through the umbilical cord to the placenta, and then into the mother’s body. She then disposes of these wastes, mainly through her kidneys and lungs.
As mentioned before, the baby float-, in a fluid sac that surrounds it, called the amniotic sac. Of course, the unborn child doesn’t drown, because it doesn’t breathe while in its mother’s uterus. It gets all the oxygen it needs from the mother through the placenta and the umbilical cord. Therefore, it isn’t necessary for it to breathe. And it doesn’t have to move its bowels either, because instead of eating through its mouth, it is getting its nourishment from the mother through the placenta and umbilical cord.
The fluid that surrounds the developing baby helps to protect it and cushions any blow that might strike it accidentally from the outside. It is rare indeed that an unborn child is injured, even if the mother has a severe fall.
At about five months along in its development, a doctor can often hear the baby’s heartbeat through a special kind of stethoscope. And by the time the fetus is six months old, it will probably be fourteen to fifteen inches long and will weigh about two pounds. At this age, all the unborn child’s organs are well formed.
So rapid is the child’s development that it gains about five pounds and grows about six inches in length during the last three months within its mother’s uterus. And the child is ready to be born when it has been inside its mother for about nine months. Some children, however, are born a month or two earlier. These are called premature babies, and they require very special care after they are born if they are to live. Occasionally, a baby is born two or three weeks late, but that doesn’t seem to matter at all.