hat is Biology Good For?
Diagnosing Problems Before Birth: Prenatal Diagnosis

(This assignment is optional. Read this essay and answer the questions at the bottom for 3 extra credit points. You may only turn in one per six weeks. The assignment is due one week before the end of the six weeks. It is not necessary to visit the links in the text unless you are interested in more information.)

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 or the developmental processes involved. However, until science has the ability to treat some of the more disastrous and ultimately fatal genetic disorders, the best remaining recourse is learning how to diagnose genetic and developmental disorders, and providing education to parents so they can make the best decisions concerning their baby's survival.

6 weeks Post-fertilization 8 weeks Post-fertilization 18 weeks Post-fertilization

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)

Why test?
Specifically, prenatal diagnosis is helpful for:

-Determining actions to take in the remaining weeks of the pregnancy
-Planning for possible complications with birth or just after birth
-Planning for surgery or therapy that may be needed for the newborn
-Deciding whether to continue the pregnancy
-Finding about inherited genetic 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.

There are a variety of techniques available for prenatal testing, including (but not limited to):
1. Ultrasound
2. Amniocentesis
3. Chorionic villus sampling (CVS)


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, 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.


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.

While some of this information sounds scary, remember that ~15,000 babies are born EVERY HOUR of EVERY DAY - that's over 128 MILLION this year! - and the vast majority are born healthy... Remember too that parents who are educated about their baby's health before birth have a better chance of getting specialized medical care, if needed, in those crucial first hours after birth.

Genetic Counseling and Prenatal Diagnosis
Genetics Center: Prenatal Diagnosis
What is Genetic Counseling?

This Good For assignment was written and researched by IUPUI Undergraduate Student Jennifer Manske as part of a Senior Research Project

The text of this "What is Biology Good For" exercise is copyrighted under the name of Dr. Kathleen A. Marrs, 1999, 2000, 2001, 2003. There are no restrictions on its use by educators or by non-profit institutions as long as its content not modified, proper copyright acknowledgement is retained, and this statement is not removed.


Extra Credit Questions: Please answer the following questions on a piece of paper and turn it into me.

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.