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McKesson Clinical Reference Systems: Women's Health Advisor 2002.2
Genetic Screening Before or During Pregnancy
What is genetic screening?
If you are concerned about illnesses in your family that a
child might inherit, you can ask your health care provider
for genetic counseling or screening. Genetic screening is a
way to learn more about diseases or birth defects that
might be inherited.
It is best to have genetic screening before you are
pregnant. However, it may also be done at your first
prenatal visit and later in your pregnancy.
A genetic counselor will ask about diseases, disorders, and
birth defects in your family. You may have blood tests.
If you are pregnant, tests of the baby may also be done.
If a genetic counselor is not available, your health care
provider may screen you.
When is it used?
Some of the reasons to have genetic screening are:
- The mother will be 35 years old or older at the time of
delivery.
- You have had a child with an inherited disease or birth
defect.
- Someone in your family has had mental retardation or
other chromosome problems.
- You have had stillbirths (babies born dead after 28
weeks of pregnancy) or several miscarriages.
- Something about the pregnancy is not normal. For
example, blood test results have been abnormal or there
is too much or not enough amniotic fluid around the
baby.
- Someone in your family has had thalassemia, a disorder
causing abnormal red blood cells. Thalassemia is most
common in people from Asia and Mediterranean countries
(for example, Italians and Greeks).
- Someone in your family has had Tay-Sachs disease, a
brain problem that can cause early death. This disease
is most common in Jews who have an Eastern European
Ashkenazic ancestry.
- Members of your family have had other inherited
problems, such as hemophilia, cystic fibrosis, or
fragile X syndrome.
- Someone in your family has had sickle cell anemia, which
causes abnormal red blood cells. This problem is most
common in North American blacks.
- The mother had diabetes before she became pregnant.
How do I prepare for genetic screening?
Learn the medical history of members of your family. Try to
get details of any inherited diseases in your family. Ask
your parents if there have been any children in their
families who have been retarded or disabled, or who had
other birth defects.
Be ready to give the following information about yourself:
- past miscarriages
- exposure to chemicals, radiation (including x-rays), or
other environmental hazards (for example, at work or from
hobbies) before or during pregnancy
- any history of drug or alcohol abuse
- prescription, nonprescription, and herbal medicines taken
during pregnancy, including before you knew you were
pregnant.
How is genetic screening done?
Your health care provider or genetic counselor will review
your family and personal medical histories.
The following tests may be used to look for birth defects
and inherited diseases when you are pregnant:
- Tests of the mother's blood, including a check of the
level of alpha fetoprotein (AFP). AFP is a protein made
by the baby. The AFP test is done between the 15th and
18th weeks of pregnancy. If the amount of AFP is high or
low, your health care provider may do other tests. The
tests look for defects in the nervous system called
neural tube defects, such as spina bifida. They also
look for chromosome defects, such as Down syndrome.
- Ultrasound scans to check the baby for birth defects of
the brain, heart, spine, legs, arms, or other organs.
- Chorionic villus sampling to test a sample of tissue from
the placenta for chromosomal problems. This test is done
between the 10th weeks and 12th weeks of a pregnancy.
- Amniocentesis to test the amniotic fluid around the baby
for abnormal chromosomes and other substances such as
alpha fetoprotein. This test is first done between the
15th and 18th weeks of a pregnancy.
- DNA sampling
- Percutaneous umbilical cord blood sampling
- Fetoscopic tissue sampling
- Fluorescent in situ hybridization for abnormal
chromosomes
Your health care provider or counselor will discuss the
screening results with you. If there is a problem, they
will help you understand the problem and describe your
choices for prevention or treatment.
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