Before
conceiving a pregnancy there are many things a couple can do to reduce the
chance of birth defects and genetic disease.
- Take Prenatal Vitamins
with folic acid before getting pregnant. Additional
information on preventing birth defects.
- Talk to a doctor about screening to determine if you are a
carrier of a genetic disease. Early identification of genetic diseases can
affect the treatment.
- Learn more about
your family medical history on both the maternal
and paternal sides of your family and your partner’s family. Write this information
down and bring it to your doctor.
- If you have concerns that
a medication, drug, or other exposure could affect your future children,
contact the Texas Teratogen Information Service Genetic counselors are
available to provide information.
Prenatal
genetic testing is one way a woman can improve the chance to have a healthy
baby. About 95% of women who have prenatal genetic testing receive good news
from the testing laboratory. Some of the tests that can look at the genetic
health of the baby include chorionic villus sampling (CVS), amniocentesis,
ultrasound, and maternal blood testing. It is important to learn all you can
about the specific procedure or test itself. It is also a good idea to know its
purpose, risks, benefits, and limitations. Below is a description of these
procedures.
Some
prenatal genetic testing like maternal blood testing is only a screening test.
A screening test will tell you that there is an increased risk for a genetic
disorder or birth defect. You may need further diagnostic testing to determine
if there is a problem. Other genetic tests like amniocentesis will tell you if
there is a specific genetic condition. These tests are all done at different
weeks of the pregnancy, so you need to talk to your doctor about prenatal
genetic testing before or early in the pregnancy.
Common Reasons for a preconception/prenatal genetic referral
- Mother will be 35 years or older at delivery
- Abnormal results from a multiple marker screen or fetal
ultrasound
- Personal or family history
of a known or suspected genetic disorder, birth defect, or chromosome
abnormality
- Exposure to a chemical/drug/environmental agent that is known or
suspected to cause a birth defect
- A mother with a medical
condition known or suspected to affect the development of the baby. (Ex.
Seizures and diabetes)
- Two or more pregnancy losses
- Close biological relationship of the parents (first cousins or
closer)
- Ethnic predisposition to certain genetic conditions
Amniocentesis
Amniocentesis is a test
that involves taking a small amount of amniotic fluid from the uterus or womb.
This fluid contains some of the baby’s skin cells that have washed off and are
floating in the fluid. The laboratory can look at these skin cells under a
microscope and learn more about the health of the baby. These cells can be
examined to detect chromosomal abnormalities or can be tested for certain
genetic conditions through DNA testing. The risk for a baby to have a
chromosome disorder increases with the woman’s age.
Mother's Age at Delivery
|
Risk for Down Syndrome
|
20
|
1/1923
|
30
|
1/885
|
31
|
1/826
|
32
|
1/725
|
33
|
1/592
|
34
|
1/465
|
35
|
1/365
|
36
|
1/287
|
37
|
1/225
|
38
|
1/177
|
39
|
1/139
|
40
|
1/109
|
41
|
>1/85
|
42
|
1/67
|
43
|
1/53
|
44
|
1/41
|
45
|
1/32
|
Chorionic Villus Sampling or CVS (placental biopsy)
CVS is a test done by
putting a small tube or catheter through the vagina and into the uterus to
remove some cells from the placenta. It can also be done by putting a needle
through the mother’s abdomen into her uterus and then into the placenta. The
doctor decides the method and depends on factors such as the location of the
placenta. The placenta has the same genetic makeup as the fetus, so testing
these cells is a way to indirectly look at the baby’s cells. This test is done
between 9 and 12 weeks of pregnancy.
Maternal Serum Screening (triple or quad screen, AFP plus,
multiple marker screen)
The maternal serum screen
is a prenatal screening test using the blood from the mother to identify women
that may be at an increased risk of carrying a baby with specific birth
defects, such as spina bifida, anencephaly, Down syndrome, and Trisomy 18. This
test is usually done on the mother’s blood between the 15 to 20 weeks of the
pregnancy and is recommended for all pregnant women.
Specific proteins or
hormones (Alpha-fetoprotein, human chorionic gonadotropin (hCG), unconjugated
estriol, and inhibin) are made by the baby or the placenta and are found in the
mother’s blood. The levels of these proteins are linked with certain birth
defects, such as spina bifida and Down syndrome. The blood test is a screening
test, meaning it cannot identify a birth defect in the baby, it only indicates
that the risk is higher and further testing is needed. A range of factors can
influence the result of the blood test, such as the gestational age of the
pregnancy or the presence of twins. It is recommended that women have an
ultrasound to confirm the pregnancy dating. If the blood test is abnormal,
further testing may be offered, such as amniocentesis or another sonogram.
Some facilities are
performing maternal serum screening tests in the first trimester. This
screening test looks at different hormones/proteins and is usually combined
with ultrasound findings. Still, others use a combination of first and second-trimester
screening. This combined testing is often called integrated screening.
Ultrasound or Sonogram
Ultrasound (also called a
sonogram) is an imaging test used to look at the fetus. It can detect some
major physical birth defects during the pregnancy, depending on the gestational
age. The test uses sound waves and poses no risk to the baby. Ultrasound can
verify how far along a woman is in her pregnancy. It also looks at fetal growth
and can detect certain problems in the baby or pregnancy. It can be done at any
time in the pregnancy, but it is usually done around 18 to 20 weeks to look for
major physical birth defects.
Nuchal Translucency Screening
A nuchal translucency
measurement is a procedure performed in the first trimester with ultrasound.
The nuchal translucency is a fluid-filled space at the back of the baby’s neck.
A large increase in nuchal translucency can be
linked with an increased risk of a baby having certain problems like Down
syndrome.
Percutaneous Umbilical Blood Sampling (PUBS, Cordocentesis,
Fetal Blood Sampling)
PUBS is a procedure where
a needle is inserted through the mother’s abdomen into the uterus and amniotic
sac and then into the baby’s umbilical cord. A sample of the baby’s blood is
removed from the umbilical cord and sent to a specialized laboratory for
analysis. The procedure is usually done when a woman is at least 20 weeks
pregnant and is usually reserved for special circumstances.
Carrier Testing for Common Conditions
Carrier testing is used to
identify individuals who carry one copy of a non-working gene (mutation) for a
certain genetic condition. Carriers are healthy and do not have the disease.
However, if both members of a couple carry a copy of the same non-working gene,
there is a 25% chance to have a child affected with that genetic condition.
Genetic carrier testing is
commonly available. Examples of available genetic carrier testing include
cystic fibrosis, sickle cell disease, thalassemia, Tay Sachs disease, Canavan
disease, and familial dysautonomia. Some conditions are more common in specific
ethnic populations (see chart below). Please consult with your doctor about
genetic carrier testing since the number of available carrier tests continues
to grow.
POPULATION
|
CONDITION
|
CARRIER FREQUENCY
|
African American
|
Sickle Cell disease
|
1 in 10
|
African American
|
Cystic fibrosis
|
1 in 65
|
African American
|
Beta thalassemia
|
1 in 75
|
Ashkenazi Jewish
|
Gaucher disease
|
1 in 15
|
Ashkenazi Jewish
|
Cystic fibrosis
|
1 in 29
|
Ashkenazi Jewish
|
Tay Sachs disease
|
1 in 30
|
Ashkenazi Jewish
|
Dysautonomia
|
1 in 32
|
Ashkenazi Jewish
|
Canavan disease
|
1 in 40
|
Asian
|
Alpha thalassemia
|
1 in 20
|
Asian
|
Beta thalassemia
|
1 in 50
|
European American
|
Cystic fibrosis
|
1 in 29
|
French Canadian, Cajun
|
Tay Sachs disease
|
1 in 30
|
Hispanic
|
Cystic fibrosis
|
1 in 46
|
Mediterranean
|
Beta thalassemia
|
1 in 25
|
University of Texas Health
Science Center in Houston
Texas Teratogen
Information on Pregnancy Service (Texas TIPS)
6431 Fannin, MSB 3.147
Houston, TX 77030
1-855-884-7248 (toll-free)
https://med.uth.edu/texastips/
Teratogen Information Databases: The Organization of Teratology
Information Specialists has compiled fact
sheets on
various exposures of concern.
Texas DSHS Newborn Screening Program