FOLK MEDICINE always had many different ways to determine what the new baby was going to "be like." If a pendulum hung over the expectant mother's stomach swung to the right, the baby would be a girl; to the left, a boy. A "high" pregnancy--that is one where the baby sits high in the mother's stomach--meant that the baby would be strong and healthy.

However, medical science has developed a new way of discovering things about the baby before its birth. These methods are certainly less picturesque but they are considered a great deal more accurate. But as they become more effective as a means of prediction, a host of attendant moral questions arise.

Amniocentesis is a process that now enables doctors to detect a certain limited number of genetic defects before birth. With the development and perfection of the technique, amniocentesis could be made widely available to determine any number of things about the fetus, including genetic defects, Rh incompatability between the fetus and the mother, and even the sex, eye color, and future height of the unborn child.

Amniocentesis is, very simply, the removal of a little fluid from the amniotic sac which surrounds the developing child. This fluid, called amniotic fluid, contains cells derived from the baby's respiratory and urinary tract. A needle is injected through the placenta and a very small amount of fluid is withdrawn. This procedure can be done in the early weeks of pregnancy. However, because of possible danger to the baby, only a very small amount of liquid can be withdrawn. The few cells obtained earlier than the 16th week must be cultured from four to eight weeks in order to assure an accurate reading of the chromosomal patterns contained therein.

IT IS THIS possibility of seeing the infant's chromosomal makeup well within the time limits required for a safe abortion that makes amniocentesis so valuable for those engaged in genetic counselling. The procedure became a viable one in the early sixties, when doctors discovered that they could determine from the amniotic fluid if there would be an Rh complication during delivery.

A baby with Rh-positive blood being carried by a mother with an Rh-negative blood runs a high risk of a complicated development and possible death because the mother's blood cells tend to destroy antibodies in the baby's blood. Using amniocentesis, the extent to which this is taking place can be determined, and if necessary, transfusions can be given to the baby. This use of amniocentesis is fairly common--thousands of pregnant women with potential Rh-incompatability are tested every year, and the necessary transfusions are performed.

In the last 25 years, medical science has made incredible discoveries in the field of genetics. Before 1948 scientists did not even know the correct number of chromosomes in the normal human body. Now that the number--46--is known, and the approximate notions of the functions of some of these chromosomes in human beings in known, doctors can determine many things about a person simply by pairing up chromosomes and observing their structures.

FOR EXAMPLE, it is well known now that female cells have two X chromosomes on the last pair. Male cells have one X and one Y. Given this information, the pregnant mother of four female children could have amniocentesis performed to determine the fetus's sex. Knowing the sex of the child in advance, the parents could decide whether or not to abort. In this way, families could maintain a balanced--or an unbalanced--male-female ratio.

And when more information is available about the functions of the different chromosomes, it is possible that the same elimination procedure could be repeated until the parents conceived the six-foot blond, blue-eyed football player they had dreamed about.

However, although it is relatively simple to determine the sex of the child, such selecting adventures are still far in the future. Less frivolous and more immediate is the possibility of eliminating genetic defects through selective abortion.

It is now possible to discover the presence of a bleeding disorder known as hemophilia. A female carrier of hemophilia will have either a normal X chromosome or a defective one--one that is linked to hemophilia. Male infants conceived from an ovum containing the defective X chromosome will be hemophiliacs. It could be perfectly simple, then, to test carriers of hemophilia, determine whether or not their babies are defective, and then depending on the wishes of the parents to abort.

ANOTHER disease which can be identified easily is Down's Syndrome, or Mongolism. A baby with Down's Syndrome generally has not a mutant gene, but an extra one, attached to the normal twenty-first chromosome pair. Procedures are under study which would enable doctors to determine accurately the presence of Tay-Sachs disease--a disease which causes blindness, severe retardation, and early death. This disease is common among Jews of northern European origin. Sickle-cell anemia is another race-linked genetic defect that could be identified and eliminated by the application of new techniques.

These new techniques--such as computerized pre-natal diagnosis which can present the physician with a rapid picture of the baby's chromosome pattern--would make the positive detection of some 30 to 40 genetic defects very possible. The advantages are obvious. With the increasing availability of abortion as a means for birth control, many people feel that if abortions can be performed on ostensibly normal but unwanted children, they can be performed on deformed children who would presumably be unwanted if the parents had foreknowledge of their defects.

However, there are certain legal and moral questions that are raised. One asks if a mother who is not willing to abort should be allowed or convined to undergo amniocentesis. If the procedure becomes very common, the discovery of a handicapped child could easily amount to an edict for abortion. The race-linkage of some defects makes members of those races understandably concerned lest amniocentesis become a potent tool of genocide in the hands of a profession dominated by white upper-class anglo-Americans.