Would you like to know more about what is happening inside of you as your baby grows? This section will tell you in a general way how this growth takes place.

The organs of reproduction

Your first menstruation was a sign that your childbearing organs were maturing. They are located in the lower part of your abdomen, placed so that each one can do its work best in relation to the others.

In the center is the uterus (womb). This is pear-shaped, hollow, and quite small, normally about 3 inches long. It narrows at the lower end into a neck-like portion called the cervix, the mouth of the womb. This, in turn, leads into the vagina, which, together with the cervix, forms a continuous passage from the uterus to the outer world. The walls of the uterus are made of thick, strong muscle. These walls expand as the baby grows and go back into place after he is born. The infant comes out through the cervix and the vagina, both of which enlarge to let him pass.

Curving away from the two upper corners of the uterus are two very small tubes, the Fallopian tubes. These lead out into your abdominal cavity, one to the right and one to the left. At the outer end, each spreads out in an umbrella-like formation close to a small almond-sized organ called an ovary. These two ovaries hold the female sex cells (the eggs, or ova)—about 300,000 in each one. Out of this large supply, only about 400 actually reach maturity during a woman's lifetime. Of these 400, only a few are finally fertilized and go on to become human beings.

How conception takes place

About every 28 days, midway between two menstrual cycles, changes take place both in the ovaries and the uterus. An ovary begins to get ready to release one of its ova. At the same time, the lining of the uterus starts to grow. Tiny glands and blood vessels appear in the top half of this lining and the whole of it becomes soft and velvety.

About 14 days before the menstrual flow, a single ovum leaves one of the ovaries, stops for about 24 hours at the entrance to a Fallopian tube, then goes on through the tube into the uterus. If conception does not take place, the lining of the uterus then gradually stops growing and comes loose. As it loosens, the blood vessels that come away with it begin to bleed. This causes the menstrual flow of blood, which lasts several days. It carries away the unused top layer of the lining of the uterus, and any other waste materials that may be present. As soon as this first menstrual period ends, preparation for another one begins. This cycle repeats itself, except during pregnancies, until the menopause, when the childbearing part of a woman's life comes to an end. Most women reach the menopause in their forties or early fifties.

When there is going to be a baby, the story is quite different. Male sex cells (spermatozoa) enter the upper vagina in millions. These cells are much smaller than the ova, and move by lashing their long slender tails. Within 10 to 20 minutes, they swim through the cervix into the uterus itself and up through the Fallopian tubes. If there is an ovum in either of the two tubes, a spermatozoan will usually succeed in entering and combining with it. This is fertilization. Conception cannot take place if the spermatozoan is late in arriving, since the ovum is capable of being fertilized for only about 12 hours after it is expelled from the ovary into one of the two Fallopian tubes.

The placenta

The fertilized egg passes through the tube into the uterus in 3 to 5 days. At the end of about 6 days, it sinks into a spot in the wall of the uterus. The layer of lining which has grown and been discarded so many times before is now receiving the fertilized egg. At this place in the lining, an organ called a placenta begins to grow. This is disc-shaped, slightly raised and covered by a transparent membrane. Blood from the mother circulates in it and so does blood from the baby (fetus).

Blood from the fetus flows in and out through two arteries and a vein. These arteries and the vein are incased in the umbilical cord, which attaches to the surface of the placenta at one end and to the baby's navel at the other. The waste products of the fetus are carried through the arteries of the umbilical cord into the placenta, where they are exchanged for oxygen and nutrients from the mother. The vein in the cord carries these materials back to the baby. The main purpose of the placenta is to make possible this interchange although it is believed to have other important functions as well. It comes out of the mother's body after the baby is born. You have probably heard it referred to as the "afterbirth."

The development of the baby in the uterus

During the first week of uterine life, your future baby is just a group of tiny cells. In the beginning there is but the one cell, formed by the union of two sex cells—a spermatozoan and an ovum. This original, single cell soon divides into two cells, which stay together. Each of these two divide, again into two, and so the process goes on. It is through this on-going cell division that all human beings grow and develop. This enlarging cluster of cells is called at first a zygote, then an embryo, then a fetus.

About two weeks after conception an embryo is still barely large enough to be seen with the naked eye. The place where a head and brain will later develop is growing very fast, however, and there are little indentations where the eyes will be.

At the end of four weeks your baby is still only about a quarter of an inch long. This is a particularly important time because now the internal organs—heart, liver, digestive system, brain and lungs—are beginning to form. The heart begins to beat, although no one will be able to hear it for many weeks. This is when you are probably beginning to think that you may be pregnant.

At five weeks the embryo is the shape of a tiny quarter-moon. His backbone has started to form. His head is growing much faster than the rest of his body, and will keep on doing so until after he is born. Tiny limb-buds appear, the beginnings of his arms and legs. At six weeks, he is almost half an inch long. The four limb-buds have grown into arms and legs.

By the seventh week ears and eye lids are forming and the internal organs are moving into place. The embryo is now floating in a sac of fluid which is sometimes called the "bag of waters." If you are wondering why he doesn't drown, there is a simple answer: He cannot because he does not use his lungs to get oxygen until he comes out into the air at birth. He gets all the oxygen he needs from your blood. The fluid keeps him evenly warm and also acts as a shock absorber to protect him from any jolts or bumps he might get from your ordinary activity.

After the eighth week the embryo is called a fetus. In the third month of pregnancy, he is about 2 1/2 inches long and weighs about an ounce. Your abdomen is beginning to enlarge. The baby's fingers and toes are usually well formed by the fourth month and tiny nails begin to show. His back is still curved like a bow, but his head is straightening up. A little hair, usually dark, is starting to grow on his scalp and his teeth are forming, deep in his gums. In both sexes, the external sex organs have now appeared. At sixteen weeks the fetus is 4 to 5 inches long and weighs about 4 ounces. His muscles are active and you may possibly feel their contractions.

Sometime during the fifth month the doctor may hear the first, faint fetal heart beat through his stethoscope. You will probably notice light fluttering movements as the fetus stretches his arms and legs. These movements begin about five calendar months before the expected time of birth, so it is well to make a note of the date. At twenty weeks the baby is about 8 inches long and 10 1/2 ounces in weight. Now your pregnancy really begins to show.

From this time on, your abdomen will get bigger quite rapidly. By the sixth month the baby's movements are real thumps. You may at times be able to see them. Sometimes he lies on one side, sometimes on the other, sometimes with his head down, sometimes with it up. When he is about seven months "along" he will probably take one position and keep it until after he leaves your body. At times you may not feel him at all. Babies have periods of waking and sleeping before they are born, just as they do afterwards.

During the last two or three months of uterine life, a baby grows "tall" very fast, gets his body fat, and rounds himself out. From the sixth month on until shortly before birth, he is covered with downy fuzz. A soft creamy substance called vernix begins to form on his body at about the seventh month.

During the eighth and ninth months he becomes more and more like the typical full-term child. The cartileges of his nose and ears develop. His nails, still paper thin, grow beyond the tips of his fingers and toes. The bones of his skull become harder and are becoming more closely knit. The hair on his head grows longer. His eyes, like the eyes of all newborn babies, are slate-blue. You will not be able to tell, when he is born, what color they will be later.

This is indeed a sketchy account of a child's growth during the first nine months or so of his existence. If you want to learn more about your baby's development, ask your physician, public health nurse or librarian to suggest some books on the subject. In a prenatal class, you will have opportunities to find out many of the things you want to know.

There are four questions of such general interest to expectant parents that it seems appropriate to try to answer them here: How does it happen that some people have twins? Can you tell beforehand whether a baby will be a boy or a girl? Can a baby be "marked" before his birth? Does it matter how old a woman is when she has her first child?

Multiple births

Doctors speak of twins, triplets and quadruplets as multiple births. It is quite rare for mothers to have three or four or more babies at the same time. Twins are more common, but your chance of having twins is only about 1 in 90. Multiple births are more frequent in some racial stocks than others and tend to run in families.

In earlier times, parents were usually taken by surprise when two or more babies appeared instead of one. Nowadays, your doctor has several ways of knowing in advance when this is going to happen. He may hear two distinct fetal heart beats or he may even feel two separate babies as he examines your abdomen. An X-ray any time after the fifth month will usually settle the matter.

There are two kinds of twins, "fraternal" and "identical." Fraternal twins are different babies from the beginning. They come from two separate cells, each one of which was separately fertilized. Each baby has its own placenta and its own bag of waters. Two such separate babies may develop either because both ovaries released a cell at the same time or because, for some reason, one ovary discharged two cells at once. These babies are just as different, one from the other, as any two brothers and sisters. Boy and girl twins are always this type, although fraternal twins may also be of the same sex.

Identical twins form in another way. They begin, as babies usually do, with the fertilization of a single ovum. But when the new single cell begins to divide, the two halves separate. Each of the two new cells thus formed has all the powers of life and growth. The two babies resulting are usually attached to the same placenta but in about 30 percent of cases each has his own. They always have separate umbilical cords and separate bags of waters. These children are always of the same sex and look so much alike that even their parents sometimes have trouble knowing which is which.

The baby's sex

A baby's sex is determined by the male cell that fertilizes the ovum. There are two kinds of male cells in almost equal proportions. One kind carries chromosome X; the other, chromosome Y. When a female cell unites with a male cell bearing the Y chromosome, the result is a boy. When the chromosome in the male cell is X, the result is a girl. Apparently it is a matter of chance which kind of male cell first reaches and fertilizes a particular female cell. There is as yet no reliable method of predicting the sex of an unborn child.

"Marking" before birth

Can a baby be "marked" before birth by his mother's thoughts, feelings or experiences? There are no nerve connections between you and your baby, so what you see, hear or think cannot affect him directly before he is born. Under some circumstances, severe and prolonged emotional disturbances may cause chemical changes in your body which affect the behavior of the uterus. Except in extreme cases, however, the baby is protected from the possible harmful influence of such changes.

There is very little chance that your baby can be affected by the shifts of mood, so characteristic of pregnancy, or the occasional outbursts that clear the air. If you are comfortable with your own feelings, your baby will be too.

Under certain conditions, tobacco smoke, alcohol, excessive fatigue and radiation may bring about changes in your body chemistry. Little is positively known, as yet, about the effects of such changes on fetal development. A moderate amount of smoking or drinking may not harm either you or your child but this is something you should check with your doctor about. In the unlikely event that radiation exposure from fallout should reach a level that calls for any special precautions, your doctor will be fully informed and can advise you.

There is no known way for a mother to instill special interests or talents into an unborn child. You may want a baby who is gifted in art or music, but no matter how faithfully and intently you may "think" music or painting or sculpture, he will have to grow in his own way. It will be much, much later before you can tell whether he has the talents you wish for him.

Age of the mother

Does the age of the mother affect her chances of a successful pregnancy? It is true that the years between 20 and 30 are usually considered optimum for childbearing. But every year, many thousands of older mothers in this country give birth, without difficulty, to healthy children. The basic reproductive processes are exactly the same for every expectant mother, regardless of the age at which she becomes pregnant.

It is true, however, that women in the older age groups have a poorer overall maternity record than the younger women. This is largely because they have lived longer and had more opportunities to develop medical problems that may complicate a pregnancy.

All maternity patients require the same thorough examinations and the same careful medical supervision, whether they are old or young. If for any reason your doctor thinks you need special attention, he will discuss his findings with you and plan with you for the kind of care you need.

Marcus Siegel

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