What is Biology Good For? Diagnosing Problems Before Birth: Prenatal Diagnosis
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For over 4000 years, certain human abnormalities have been noted to run in families, but the “how” and “why” did not become apparent until the advent of modern genetics. But, by understanding DNA, genes, and chromosomes, present day medicine has been able to recognize the way these diseases are inherited. However, until science has the ability to treat some of the more disastrous and ultimately fatal genetic disorders, the best remaining recourse is prevention, such as prenatal diagnosis.
Three to four out of every 100 babies are born with some type of birth defect, either major or minor. Some of these birth defects can be prevented, most cannot. However, many can be detected before birth. This process of testing for birth defect during pregnancy is referred to as prenatal diagnosis. Identifying certain birth defects before a baby is born may enable a couple and their doctor to make informed decisions regarding the pregnancy. (geneticscenter.com) There are a variety of techniques available for prenatal testing, including (but not limited to): 1. Ultrasound 2. Amniocentesis 3. Chorionic villus sampling (CVS) Why test? Specifically, prenatal diagnosis is helpful for: -Managing the remaining weeks of the pregnancy -Determining the outcome of the pregnancy -Planning for possible complications with the birthing process -Planning for problems that may occur in the newborn infant -Deciding whether to continue the pregnancy -Finding conditions that may affect future pregnancies Who should be tested? Not every pregnant woman should or needs to be tested. However, prenatal diagnosis is highly recommended for those parents at an increased risk of having an infant with a genetic disorder. These test may also be suggested if the woman is 35 years of age or older – women over age 35 have an increased risk of having a baby with a chromosome abnormality, such as Down syndrome. Prenatal diagnosis my also be useful if a previous child was born with a disorder or if either parent are known carriers of a genetic disorder. ULTRASOUND An ultrasound, or “sonogram,” is a test that uses high frequency sound waves to produce a visible image of the baby. (The pattern of echoes coming from different tissues and organ, including the fetus, is what creates this image) This non-invasive technique is the most common method used for detecting fetal abnormalities, as it is harmless to both fetus and mother. While ultrasound does not provide a crystal clear picture of the baby, by 16-18 weeks of pregnancy, a doctor can identify certain physical abnormalities, heart defects, and some abnormalities of the brain and spine. This test is mostly limited to identifying problems of a physical or structural nature and cannot detect problems of function (e.g. mental retardation, blindness, deafness) or of chromosome abnormality (e.g. Down syndrome). AMNIOCENTESIS Amniocentesis, usually performed at 15-20 weeks of pregnancy, is the procedure by which amniotic fluid, which surrounds the fetus, is obtained for studies. This test involves placing a very fine needle through the woman’s abdomen and into the amniotic sac for sample. The amniotic fluid withdrawn contains fetal skin cells that contain the genetic material of the fetus. These cells are grown in culture and then analyzed for chromosome abnormalities, genetic disorders and open neural tube defects. Amniocentesis has risks, however, when performed by an experienced doctor, the risk for complications is generally less than one percent. CHORIONIC VILLUS SAMPLING (CVS) CVS is a prenatal diagnostic test used to identify chromosome abnormalities and certain other genetic disorders in the baby as early as 10-12 weeks of pregnancy. CVS is not, however, useful for detecting open neural tube disorders. The test involves sampling placental tissue (chorionic villi) by either of two methods. (The placenta is nourishment for the baby). In one method, the sample is obtained by inserting a catheter (a thin tube) is into the woman’s vagina, through the cervix, and into the placenta. The other method involves inserting a needle into the woman’s abdomen to withdraw the sample. The main benefit with CVS is that the results are available earlier than with amniocentesis. The disadvantage, on the other hand, is that it is an invasive procedure, and therefore has a small rate of morbidity for the fetus. Also, studies suggest that CVS has about a 0.5-1.0% greater risk than amniocentesis for miscarriage.
References: Genetic Counseling and Prenatal Diagnosis Genetics Center: Prenatal Diagnosis Prenatal Diagnosis
This Good For assignment was by IUPUI Undergraduate Student Jennifer Manske as part of a Senior Research Project ------------------------------------------------------------------------------------------------------------
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1. List one benefit of ultrasound. 2. What is the relative risk for a pregnant woman of age 32 to give birth to a baby with Down syndrome? (Scroll down to Risk and Maternal Age) 3. Name one benefit and one drawback about the CVS procedure.
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