A. Describe the AFP (alpha-fetoprotein test as a screening test.
B. Discuss karyotyping in pre-natal diagnosis. Prepare karyotypes.
C. Discuss fetal transfusions for Rh incompatability.
D. Discuss the use of genetic counseling.
E. Cite the implications of genetic engineering.
There are several methods for screening and pre-natal diagnosis. One of these can detect the presence of alphafetoprotein (AFP), a substance produced by the baby and passed into the mother’s blood and the amniotic fluid.
A blood test is offered between the 15th and 20th weeks of pregnancy. It can tell a woman: 1) that she may be carrying twins; 2) that the pregnancy is further along then she thought and she could deliver earlier and 3) that she may have a baby with a neural tube defect such as spina bifida (open spine) or anencephaly (lack of cover of brain).
If the test is positive a second test, ultrasound (obtaining a picture of the fetus by using sound waves) is used to determine how long is the pregnancy or whether there are twins. If ultrasound does not explain the abnormal AFP, amniocentesis (withdrawal of amniotic fluid) is performed. One in 15 at this point will prove to have spina bifida or anencephaly.
The AFP test is not perfect and a negative test is not conclusive. It detects most cases of anencephaly but only 80% of open spina bifida.
Recently, a test has been developed to find out if a fetus has normal or abnormal chromosomes. The test consists of a special analysis of amniotic fluid obtained by an established medical procedure called amniocentesis. The amniotic fluid contains cells shed by the fetus. These cells are allowed to grow and multiply in cultures in a laboratory until there are enough for analysis. The cells are analyzed to determine the chromosomal pattern of the fetus This is done by karyotyping which is the photographing and grouping of the chromosomes obtained from the cultured cells. For a more detailed explanation see Appendix 3.
If the results of the test show normal chromosomes, some of the worry of the expectant parents can be eliminated. If the results show abnormal chromosomes indicating severe birth defects, the option of elective abortion is available. Amniocentesis is best performed during the 16th to 18th week after the first day of the mother’s last menstrual period.
There are many birth defects for which pre-natal testing is not available. Examples of these include cleft lip and palate, congenital heart defects and cystic fibrosis. Consequently, a normal result from pre-natal chromosome and AFP testing will not guarantee a normal baby.
Fetal transfusions are used to treat cases of Rh incompatability. Rh incompatability exists if the mother is Rh negative (-) and the fetus is Rh positive (+). Small amounts of the fetal blood can cross the placental barrier and reach the mother’s blood which is stimulated to build anti-Rh antibodies if she has previously been sensitized to Rh + cells. These antibodies then travel back into the baby and attach to its cell destroying them. The baby can be transfused in utero or immediately at birth. A first pregnancy with a Rh + fetus rarely leads to this blood problem. The probability increases with subsequent Rh + pregnancies. The Rh-mother can now be treated with anti-Rh globulin when she delivers an Rh+ baby to prevent sensitization.
Genetic counseling is available and a useful tool to deal with genetic disorders. The aim of genetic counseling is to convey to an affected or potentially affected family the medical and genetic facts and to explain the medical options that may be available. It requires a person or a team of persons skilled in genetics and medicine. They will be dealing with persons who may show anger, shock, despair and guilt. The procedures may include medical diagnosis, including karyotype analysis, pedigree analysis, estimating risks, options and follow-up and supportive services. It may also involve examining the couples own values with the most information and support.
Genetic engineering that involves the manipulation of genes or gametes, i.e., recombinant DNA techniques, in vitro fertilization and cloning is still in its formative stages. How useful it can be will depend on how much it can improve the quality of human life.
The tools and the technology are here; and so is the knowledge to use them. There is still much to be learned. How all of this will be handled in the future may involve some serious medical, philosophical and ethical decisions.