American Medical Association Family Medical Guide - American Medical Association [661]
These prenatal diagnostic tests pose a slight risk to the developing fetus, including infection of the uterus and miscarriage. A genetic counselor will help you evaluate the risks and benefits of having these tests and weigh them against your risk of transmitting a genetic disorder to a child. This information will enable you to make decisions about whether you are willing to undergo the possible risk to your fetus that the test might confer and whether you would choose to terminate the pregnancy if you learn that the fetus has a serious disorder.
A genetic counselor will discuss with you the potential severity of the particular genetic disorder you may be at risk of passing on to a child, treatments that may be available for the disorder, and the effectiveness of these treatments. Many people decide not to have prenatal diagnostic tests, and accept the possibility that their child may be born with a genetic disorder or defect. Other people who would not choose to terminate a pregnancy decide to have the test so they can be prepared to care for a child with a genetic disorder or birth defect.
Who Should Seek Genetic Counseling?
Genetic counseling can help people understand their chances of passing on a genetic disorder or birth defect to children or of developing a particular disorder themselves. Consider genetic counseling if you have any of the following risk factors:
• You (or your partner) have a family history of a genetic disorder or birth defect.
• You have a child who was diagnosed at birth with a genetic disorder or birth defect.
• Your doctor has told you that you may be at risk of having children with birth defects or genetic disorders.
• You are a woman over age 35 who is pregnant or planning to become pregnant. (Being over 35 increases a woman’s risk of having a child with a chromosome abnormality such as Down syndrome.)
• You have had a baby who died in infancy or you have had two or more miscarriages.
• You have been exposed to toxic chemicals, high doses of radiation, or other environmental factors that might increase your risk of having a child with birth defects.
• You are planning to have children with a person who is a close blood relative, such as a first cousin.
Genetic Testing
As scientists identify more and more genes linked to diseases and disorders, people increasingly will be offered the option of having a test to determine if they carry a particular gene or genes for a specific disorder. The more you know about how diseases can be passed from one generation to the next, or how having specific genes may make you susceptible to developing a disease such as heart disease later in life, the better prepared you will be to make decisions about planning a family and to make good lifestyle choices. Following are brief descriptions of some of the genetic tests that are available.
Prenatal Testing
During pregnancy, women are given the option to have testing to determine if their fetus has a genetic abnormality or birth defect. One of these tests examines a pregnant woman’s blood for the level of a protein called alpha-fetoprotein (AFP; see page 510). AFP is normally present in the blood, but a higher-than-average level of the protein indicates that the fetus may have a brain or spinal cord defect such as spina bifida. A lower-than-average level of AFP, when combined with altered levels of other proteins—human chorionic gonadotropin (hCG) and unconjugated estriol (uE3)—may indicate that the fetus has Down syndrome.
Chorionic villus sampling, or CVS (see page 511), removes a small sample of tissue from the placenta for analysis; amniocentesis (see page 510) takes a sample of amniotic fluid for analysis. Ultrasound (see page 509) uses high-frequency sound waves to produce an image of the