At one time it was believed that the fetus was unable to sense much of anything while in utero, however, due to modern research we are reasonably sure that the fetus can touch, taste, smell, hear and see. Although at birth these senses may be considered primitive, they are in fact all operative.
Touch-the first sensation of touch appears in the skin of the face and gradually progresses downward over the rest of the body.
Taste-the taste buds appear in the third month and are fully developed by about the seventh month. One researcher showed differences in amount of amniotic fluid ingested by the fetus when saccharine was introduced into the amniotic sac.
Smell-premature infants have an olfactory sense; this was demonstrated when they turned their heads away from foul smells.
Hearing-fetuses have been found to react to very loud noises in utero.
Vision-a full-term infant is capable of visually following a slow moving object,even premature babies are apparently capable of distinguishing between light and dark.
. Of all the babies born in one year in the United States, 94% are perfectly healthy. But 6% have some form of birth defect. Many other pregnancies terminate before the end of the ninth month period for a variety of medical and genetic reasons. Specifically in the United States:
Genes and Genetic Counseling
—3.3 million babies are born each year, of these 700 per day are afflicted with a birth defect.
—15 million people have suffered from a birth defect; 20% of these individuals are mentally retarded.
—500,000 conceptions never result in live births.
—1,500,000 preschoolers who suffer from defects have spent six million days in the hospital at a cost of $180 million each year.
—200,000 families have been affected by birth defects.
—18,000 babies die of birth defects before their first birthdays.
—genetic defects are the cause of 20,000,000 future life years being lost.
—1/5th of all birth defects have genetic implications.
—abnormal prenatal management is the cause of 50% of all mentally defective children.
—50% of all the mentally defective children in the previous statistic could have been normal if prenatal environment were improved.
. In the beginning there is a merging of 23 chromosomes from the mother, contained in the egg, and 23 chromosomes from the father, contained in the sperm. Each child created by this union will have a full complement of 46 chromosomes of 23 pairs. Chromosomes can subdivide into small units, genes, which are the biochemical instructions for an individual’s traits.
Genes are classified as either dominant or recessive. Usually if a trait appears in the new offspring it is dominant. For example, if a father has black hair and the mother has blond hair, the dominant is black. Therefore, chances are good that the baby will have black hair. The implications of dominant and recessive genes on birth defects are important because if both parents are carriers of a recessive gene that causes a birth defect, the chances for it to surface in one of their offspring are about 25%.
The chart on the next page demonstrates how inheritance of genetic traits works.
If during a genetic work-up a birth defect is detected in the fetus the family can be given alternatives, including a cure if one is available. Genetic work-ups include, a paternal and maternal family history, ultrasound, fetoscopy, and amniocentesis.
Amniotic Fluid and Amniocentesis
. At about the eighth week of conception the amniotic sac has developed. This sac is a pouch of saline fluid in which the embryo develops over the duration of the pregnancy.
The amniotic fluid contains cells and chemicals that are sloughed off from the developing embryo. The cells are from the embryo’s skin, while the chemicals come from the urine and lungs.
Out of the need for better genetic screening, a procedure known as amniocentesis was developed. The way in which this is done is as follows: first, it is performed by an obstetrician, who uses a local anesthetic to numb the mother’s abdomen. Next the doctor inserts a long thin needle through the abdomen wall and uterine wall and into the amniotic sac, where it draws in a small amount of that saline solution.
(figure available in print form)
NINE MONTH FETUS JUST BEFORE LEAVING THE WOMB
(figure available in print form)
To guide the doctor during this procedure, ultrasound is used. Ultrasound is employed to locate the exact positions of the embryo and the placenta, this is done so as not to puncture either. The optimum time for amniocentesis is about the sixteenth week of gestation.
After the fluid is drawn, special tests are required for the detection of any abnormality. The fluid is spun in a centrifuge to separate all the different substances. The chemicals are then scrutinized for any abnormalities, these chemicals reveal information about the central nervous system and its development. If abnormal quantities of certain chemicals are present, we are almost certain that the increased amount is caused by some abnormality either in the brain and skull or the spine and spinal cord.
Amniocentesis can also be used to identify the sex of the embryo. This is important because there are certain diseases which are sex linked (check chart on page 7); that is they may only be inherited by a male embryo.
Even though this method of early detection is available, it is not always administered upon request, because of the uncertainty of its effects on the developing embryo. At this time the National Institute of Child Health is conducting an in depth study with 1,040 women who underwent amniocentesis. They are comparing the results of these pregnancies with the results of 992 other pregnant women who did not have this procedure performed. Early findings do not indicate any negative aftereffects due to amniocentesis. The investigators also found that in 99% of the cases amniocentesis predicted the presence of a defect in the embryo.
As mentioned earlier, amniocentesis is fine for detecting genetic and chemical defects, but not developmental abnormalities that occur physically, such as were evident during the 1960’s with the use of thalidomide. These physical problems can now be detected through the use of fetoscopy.
is a tiny tube with a fiberoptic instrument on the end of it. Through this instrument the doctor can observe the developing fetus. This tool is used during the third stage of embryonic growth, the fetal stage. The tube is inserted in the same manner as the needle used in amniocentesis. The fetoscope has a side arm attached to it through which another needle can be brought down to draw blood from the fetus or to take skin scrappings. The blood will assist the doctor in determining the presence of sickle-cell disease or Tay Sachs Disease. This is a new procedure which up until recently was employed only at the Yale Medical Center and the University of California at San Francisco.
Another device mentioned earlier and used in conjunction with amniocentesis or by itself is ultrasound. This instrument sends out harmless sound waves—these are so high in pitch that they are not detectable by the human ear. The instrument bounces these waves off the mother’s abdomen and when the waves hit various internal organs or fluid they bounce off in different ways and strike a detector. The detector uses these waves to form a black and white picture of the site of the placenta and embryo. This is used instead of an x-ray machine because radiation exposure can cause birth defects in the unborn.