Every parent-to-be hopes for a healthy baby, but it can be hard
not to worry: What if the baby has a serious or untreatable
health problem? What would I do? Is there anything I can do to
prevent problems?
Concerns like these are completely natural. Fortunately, though,
a wide array of tests for pregnant women can help to reassure them
and keep them informed throughout their pregnancies.
Prenatal tests can help identify health problems that could
endanger both you and your unborn child, some of which are
treatable. However, these tests do have limitations. As an
expectant parent, it's important to educate yourself about them
and to think about what you would do if a health problem is
detected in either you or your baby.
Why Are Prenatal Tests Performed?
Prenatal tests can identify several different things:
- treatable health problems in the mother that can affect the
baby's health
- characteristics of the baby, including size, sex, age, and
placement in the uterus
- the chance that a baby has certain congenital, genetic, or
chromosomal problems
- certain types of fetal abnormalities, including some heart
problems
The last two items on this list may seem the same, but
there's a key difference. Some prenatal tests are screening
tests and only reveal the
possibility
of a problem. Other prenatal tests are diagnostic, which means
they can determine - with a fair degree of certainty - whether a
fetus has a specific problem. In the interest of making the more
specific determination, the screening test may be followed by a
diagnostic test.
Prenatal testing is further complicated by the fact that more
abnormalities can be diagnosed in a fetus than can be treated or
cured.
What Do Prenatal Tests Find?
Among other things, routine prenatal tests can determine key
things about the mother's health, including:
- her blood type
- whether she has gestational diabetes
- her immunity to certain diseases
- whether she has a sexually transmitted disease (STD) or
cervical cancer
All of these conditions can affect the health of the fetus.
Prenatal tests also can determine things about the fetus'
health, including whether it's one of the 2% to 3% of babies in
the United States that the American College of Obstetricians and
Gynecologists (ACOG) says have major congenital birth defects.
Tests for Disorders
Categories of defects which can be picked up by prenatal tests
include the following disorders:
Dominant Gene Disorders
In dominant gene disorders when one parent is affected,
there's a 50-50 chance a child will inherit the gene from the
affected parent and have the disorder.
Dominant gene disorders include:
-
Achondroplasia
, a rare abnormality of the skeleton that causes a form of
dwarfism, can be inherited from a parent who has it, but most
cases occur without a family history.
-
Huntington disease
, a disease of the nervous system that causes a combination of
mental deterioration and a movement disorder.
Recessive Gene Disorders
Because there are so many genes in each cell, everyone carries
some abnormal genes, but most people don't have a defect
because the normal gene overrules the abnormal recessive one. But
if a fetus has a pair of abnormal recessive genes (one from each
parent), the child will have the disorder. It can be more
likely for this to happen in children born to certain ethnic
groups.
Recessive gene disorders include:
-
Cystic fibrosis
, most common among people of northern European descent, this
disease is life threatening and causes severe lung damage and
nutritional deficiencies.
-
Sickle cell disease
, most common among people of African descent, is a
disease in which red blood cells form a "sickle"
shape (rather than the typical donut shape) that can get caught
in blood vessels and damage organs and tissues.
-
Tay-Sachs disease
, most common among people of eastern European (Ashkenazi) Jewish
descent, can cause mental retardation, blindness, seizures, and
death.
-
Beta-thalassemia
, most common among people of Mediterranean descent, this
disorder can cause anemia.
X-Linked Disorders
These disorders are determined by genes on the X chromosome. The
X and Y chromosomes are the chromosomes that determine sex. These
disorders are much more common in boys because the pair of sex
chromosomes in males contains only one X chromosome (the other is a
Y chromosome). If the disease gene is present on the one X
chromosome, the X-linked disease shows up because there's no
other paired gene to "overrule" the disease gene. One
such X-linked disorder is
hemophilia
, which prevents the blood from clotting properly.
Chromosomal Disorders
Chromosomal disorders occur when there is an abnormality in the
number or structure of chromosomes, which contain the genetic
material. Some chromosomal disorders are inherited but most are
caused by a random error in the genetics of the egg or sperm. The
chance of a child having these disorders increases with the age of
the mother. For example, according to ACOG, 1 in 1,667 live babies
born to 20-year-olds have Down syndrome, which causes mental
retardation and physical defects. That number changes to 1 in 378
for 35-year-olds and 1 in 106 for 40-year-olds.
Multifactorial Disorders
This final category includes disorders that are caused by a mix
of genetic and environmental factors. Their frequency varies from
location to location, and some can be detected during
pregnancy.
Multifactorial disorders include neural tube defects, which
occur when the tube enclosing the spinal cord doesn't form
properly. Neural tube defects, which often can be prevented by
taking
folic acid
(which is in prenatal vitamins) around the time of conception and
during pregnancy, include:
-
Spina bifida
.
Also called "open spine," this defect happens when the
lower part of the neural tube doesn't close during embryo
development. The spinal cord and nerves may be covered only by
skin, or may be open to the environment, leaving them
unprotected.
-
Anencephaly.
This defect occurs when the brain and head don't develop
properly, and parts of the brain are completely absent
or malformed.
Other multifactorial disorders include:
Who Has Prenatal Tests?
Certain prenatal tests are considered routine - that is, almost
all pregnant women receiving
prenatal care
get them. Other nonroutine tests are recommended only for certain
women, especially those with high-risk pregnancies. These may
include women who:
- are age 35 or older
- are adolescents
- have had a
premature baby
- have had a baby with a birth defect - especially heart or
genetic problems
- are carrying more than one baby
- have high blood pressure, diabetes,
lupus
, heart disease, kidney problems, cancer, a sexually transmitted
disease,
asthma
, or a seizure disorder
- have an ethnic background in which genetic disorders are
common (or a partner who does)
- have a family history of mental retardation (or a partner who
does)
Although your health care provider (which may be your OB-GYN,
family doctor, or a certified
nurse-midwife
) may recommend these tests, it's ultimately up to you to
decide whether to have them.
Also, if you or your partner have a family history of genetic
problems, you may want to consult with a
genetic counselor
to help you look at the history of problems in your family, and to
determine the risk to your children.
To decide which tests are right for you, it's important to
carefully discuss with your health care provider:
- what these tests are supposed to measure
- how reliable they are
- the potential risks
- your options and plans if the results indicate a disorder or
defect
Prenatal Tests During the First Visit
During your first visit to your health care provider for
prenatal care, you can expect to have a full physical, which may
include a pelvic and rectal examination, and you'll
undergo certain tests regardless of your age or genetic
background.
You may have a urine test to check for protein, sugar, or signs
of infection.
Blood tests check for:
- your blood type and
Rh factor
. If your blood is Rh negative and your partner's is Rh
positive, you may develop antibodies that prove dangerous to your
fetus. This can be prevented through a course of injections given
to you.
-
anemia
(a low red blood cell count)
-
hepatitis B
,
syphilis
, and
HIV
- immunity to
German measles
(rubella) and
chickenpox
(varicella)
- cystic fibrosis. Health care providers now
routinely offer this screening even when there's no
family history of the disorder.
Cervical tests (also called Pap smears) check for:
- STDs such as chlamydia and gonorrhea
- changes that could lead to cervical cancer
To do a Pap smear, your health care provider uses what looks
like a very long mascara wand or cotton swab to gently scrape the
inside of your cervix (the opening to the uterus that's located
at the very top of the vagina). This may be a little uncomfortable,
but it is over quickly.
Prenatal Tests Performed Throughout or Later in Pregnancy
After the initial visit, your health care provider will order
other tests based on, among other things, your personal medical
history and risk factors, as well as the current recommendations.
These tests may include:
- Urine tests for sugar, protein, and signs of infection. The
sugar in urine may indicate gestational diabetes - diabetes that
occurs during pregnancy; the protein can indicate preeclampsia -
a condition that develops in late pregnancy and is characterized
by a rise in blood pressure, with fluid retention and protein in
the urine.
- Group B
streptococcus
(GBS) infection. GBS bacteria are found naturally in the vaginas
of many women but can cause serious infections in newborns. This
test involves swabbing the vagina and rectum, usually between the
35th and 37th weeks of pregnancy. If the test comes back
positive, it is important to go to the hospital as soon as your
labor begins so that intravenous antibiotics can be started in
order to reduce the chance of the baby being infected.
- Sickle cell trait tests for women of African or Mediterranean
descent, who are at higher risk for having sickle cell anemia - a
chronic blood disease - or carrying the trait, which can be
passed on to their children.
Other Tests
Here are some other tests that might be performed during
pregnancy:
Ultrasound
Why Is This Test Performed?
In this test, sound waves are bounced off the baby's bones
and tissues to construct an image showing the baby's shape and
position in the uterus.
Ultrasounds
were once used only in high-risk pregnancies but have become so
common that they're often part of routine prenatal care.
Also called a sonogram, sonograph, echogram, or ultrasonogram,
an ultrasound is used:
- to determine whether the fetus is growing at a normal
rate
- to verify the expected date of delivery
- to record fetal heartbeat or breathing movements
- to see whether there might be more than one fetus
- to identify a variety of abnormalities that might affect the
remainder of the pregnancy or delivery
- to make sure the amount of amniotic fluid in the uterus is
adequate
- to indicate the position of the placenta in late pregnancy
(which may be blocking the baby's way out of the uterus)
- to detect pregnancies outside the uterus
- as a guide during other tests such as amniocentesis
Ultrasounds also are used to detect:
- structural defects such as spina bifida and anencephaly
- congenital heart defects
- gastrointestinal and kidney malformations
- cleft lip or palate
Should I Have This Test?
Most women have at least one ultrasound. The test is considered
to be safe. Some women will have multiple ultrasounds during the
pregnancy, others do not have any. Ask your health care provider if
he or she thinks you will have ultrasounds during your
pregnancy.
When Should I Have This Test?
An ultrasound is usually performed at 18 to 20 weeks to look at
your baby's anatomy. If you want to know your baby's
gender, you may be able to find out during this time - that is, if
the genitals are in a visible position.
Ultrasounds also can be done sooner or later and sometimes more
than once, depending on the health care provider and the pregnancy.
For example, some providers will order an ultrasound to date the
pregnancy, usually during the first 3 months. And others may want
to order one during late pregnancy to make sure the baby's
turned the right way before delivery.
Women with high-risk pregnancies may need to have multiple
ultrasounds using more sophisticated equipment. Results can be
confirmed when needed using special three-dimensional (3-D)
equipment that allows the technician to get a more detailed look at
the baby.
How Is This Test Performed?
Women need to have a full bladder for a transabdominal
ultrasound (an ultrasound of the belly) to be performed in the
early months - you may be asked to drink a lot of water and not
urinate. You'll lie on an examining table and your abdomen will
be coated with a special ultrasound gel. A technician will pass a
wand-like instrument called a transducer back and forth over your
abdomen. You may feel some pressure as the technician presses on
the bladder. High-frequency sound waves "echo" off your
body (and the fetus) and create a picture of the fetus inside
on a computer screen.
You may want to ask to have the picture interpreted for you,
even in late pregnancy - it often doesn't look like a baby to
the untrained eye.
Sometimes, if the technician isn't able to see a good
enough image from the ultrasound, he or she will determine that a
transvaginal ultrasound is necessary. This is especially common in
early pregnancy. For this procedure, your bladder should be empty.
Instead of a transducer being moved over your abdomen, a slender
probe called an endovaginal transducer is placed inside your
vagina. This technique often provides improved images of the uterus
and ovaries.
Some health care providers may have the equipment and trained
personnel necessary to provide in-office ultrasounds, whereas
others may have you go to a local hospital or radiology center.
Depending on where you have the ultrasound done, you may be able to
get a printed picture (or multiple pictures) of your baby and/or a
disc of images you can view on your computer and even send to
friends and family.
When Are the Results Available?
Although the technician can see the images immediately, a full
evaluation by a physician may take up to 1 week.
Depending on where you have the ultrasound done, the technician
may be able to tell you that day whether everything looks OK.
However, most radiology centers or health care providers prefer
that technicians not comment until a specialist has taken a look -
even when everything is OK.
Glucose Screening
Why Is This Test Performed?
Glucose screening checks for gestational diabetes, a short-term
form of diabetes that develops in some women during pregnancy.
Gestational diabetes is increasing in frequency in the United
States, and may occur in 3 to 8% of pregnancies. Gestational
diabetes can cause health problems for the baby, especially if it
is not diagnoses or treated.
Should I Have This Test?
Most women have this test in order to diagnose and treat
gestational diabetes, reducing the risk to the baby.
When Should I Have This Test?
Screening for gestational diabetes usually takes place at 24 to
28 weeks. Testing may be done earlier for women who are at higher
risk of having gestation diabetes, such as those who:
- have previously had a baby that weighs more than 9 pounds
(4.1 kilograms)
- have a family history of diabetes
- are obese
- are older than age 25
- have sugar in the urine on routine testing
- have high blood pressure
- have polycystic ovary syndrome
How Is the Test Performed?
This test involves drinking a sugary liquid and then having your
blood drawn after an hour. If the sugar level in the blood is high,
you'll have a glucose-tolerance test, which means you'll
drink a glucose solution on an empty stomach and have your blood
drawn once every hour for 3 hours.
When Are the Results Available?
The results are usually available within 1 to 2 days. Ask
if your health care provider will call you with the results if they
are normal or only if the reading is high and you need to come in
for another test.
Chorionic Villus Sampling (CVS)
Why Is This Test Performed?
Chorionic villi are tiny finger-like units that make up the
placenta (a disk-like structure that sticks to the inner lining of
the uterus and provides nutrients from the mother to the fetus
through the umbilical cord). They have the same chromosomes and
genetic makeup as the fetus.
This alternative to an amniocentesis removes some of the
chorionic villi and tests them for chromosomal abnormalities, such
as Down syndrome. Its advantage over an amniocentesis is that it
can be performed earlier, allowing more time for expectant parents
to receive counseling and make decisions. The risks of CVS are
higher than with amniocentesis so the risks and benefits of the
test must be weighed.
Should I Have This Test?
Your health care provider may recommend this test if you:
- are older than age 35
- have a family history of genetic disorders (or a partner who
does)
- have a previous child with a genetic disorder or had a
previous pregnancy with a chromosomal abnormality
- have had an earlier screening test that indicates that there
may be a concern
Possible risks of this test include:
- approximately 1% risk of miscarriage (the risk is higher with
the transcervical method than with the transabdominal
method)
- infection
- spotting or bleeding (this is more common with the
transcervical method - see below)
- birth defects when the test is done too early in
pregnancy
When Should I Have This Test?
At 10 to 12 weeks.
How Is This Test Performed?
This test is done in one of two ways:
-
Transcervical.
Using ultrasound as a guide, a thin tube is passed from the
vagina into the cervix. Gentle suction removes a sample of tissue
from the chorionic villi. Some women experience cramping with the
removal.
-
Transabdominal.
A needle is inserted through the abdominal wall with ultrasound
guidance, and a sample of the chorionic villi is removed.
Cramping may be felt with this approach as well.
After the sample is taken, the doctor may check the fetus'
heart rate. You should rest for several hours afterward.
When Are the Results Available?
Usually 1 to 2 weeks depending on what the test is being used to
look for.
Maternal Blood Screening/Triple Screen/ Quadruple Screen
Why Is This Test Performed?
Doctors use this to test to screen for Down syndrome and neural
tube defects. Alpha-fetoprotein (AFP) is a protein produced by the
fetus, and it appears in varying amounts in the mother's blood
and the amniotic fluid at different times during pregnancy. A
certain level in the mother's blood is considered normal, but
higher or lower levels may indicate a problem.
This test also looks at the levels of two pregnancy
hormones - estriol and human chorionic gonadotropin (HCG) - which
is why it's sometimes called a "triple screen" or
"triple marker." The test is called a "quadruple
screen" ("quad screen") or "quadruple
marker" ("quad marker") when the level of an
additional substance - inhibin-A - is also measured. The greater
number of markers increases the accuracy of the screening and
better identifies the possibility of a problem.
This test, which also is called a
multiple-marker screening
or maternal serum screening, calculates a woman's individual
risk based on the levels of the three (or more) substances
plus:
- her age
- her weight
- her race
- whether she has diabetes requiring insulin treatment
- whether she is carrying one fetus or multiple ones
Sometimes this test is done along with an ultrasound and blood
work during the first trimester, which makes it even more accurate
than the second trimester blood work alone.
It's important to note, though, that each of
these screening tests determine risk only - they don't
diagnose a condition.
Should I Have This Test?
All women are offered some form of this test. Some practitioners
include more parts of it than others. Remember that this is a
screening, not a definitive test - it indicates whether a woman is
likely to be carrying an affected fetus. It's also not
foolproof - Down syndrome, another chromosomal abnormality, or a
neural tube defect may go undetected, and some women with abnormal
levels have been found to be carrying a healthy baby. Further
testing is recommended to confirm a positive result.
When Should I Have This Test?
The blood tests are typically done between 15 and 20 weeks. When
first trimester screening is added, the initial tests are done at
about 11 to 13 weeks.
How Is the Test Performed?
Blood is drawn from the mother. When first trimester screening
is added, an ultrasound is included.
When Are the Results Available?
Usually within a week, although it may take up 2 weeks.
Amniocentesis
Why Is This Test Performed?
This test is most often used to detect:
- Down syndrome and other chromosome abnormalities
- structural defects such as spina bifida and anencephaly
- inherited metabolic disorders
Late in the pregnancy, this test can reveal if a baby's
lungs are strong enough to allow the baby to breathe normally after
birth. This can help the health care provider make decisions about
inducing labor or trying to prevent labor, depending on the
situation. For instance, if a mother's water breaks early, the
health care provider may want to try to hold off on delivering the
baby as long as possible to allow for the baby's lungs to
mature.
Other common birth defects, such as heart disorders and cleft
lip and palate, can't be determined using this test.
Should I Have This Test?
Your health care provider may recommend this test if you:
- are older than age 35
- have a family history of genetic disorders (or a partner who
does)
- have a previous child with a birth defect, or had a previous
pregnancy with a chromosomal abnormality or neural tube
defect
- had an abnormal screening test
This test can be very accurate - close to 100% - but only
certain disorders can be detected. The rate of miscarriage with
this procedure is between 1 in 300 and 1 in 500. It also carries a
low risk of uterine infection, which can also cause miscarriage,
leakage of amniotic fluid, and injury to the fetus.
When Should I Have This Test?
Amniocentesis is usually performed between 15 and 20 weeks.
How Is the Test Performed?
While watching with an ultrasound, the doctor inserts a needle
through the abdominal wall into the uterus to remove some (about 1
ounce) of the amniotic fluid. Some women report that they
experience cramping when the needle enters the uterus or pressure
while the doctor retrieves the sample.
The doctor may check the fetus' heartbeat after the
procedure to make sure it's normal. Most doctors recommend rest
for several hours afterwards.
The cells in the withdrawn fluid are grown in a special culture
and then analyzed (the specific tests conducted on the fluid depend
on personal and family medical history).
When Are the Results Available?
Timing varies; depending on what is being tested for, the
results are usually available within 1 to 2 weeks. Tests of lung
maturity are often available within a few hours.
Nonstress Test
Why Is This Test Performed?
A nonstress test (NST) can determine if the baby is responding
normally to a stimulus. Used mostly in high-risk pregnancies or
when a health care provider is uncertain of fetal movement, an NST
can be performed at any point in the pregnancy after the 26th to
28th week when fetal heart rate can appropriately respond by
accelerating and decelerating.
This test may also be done if you've gone beyond your due
date. The NST can help a doctor make sure that the baby is
receiving enough oxygen and is responding to stimulation. However,
an unresponsive baby isn't necessarily in danger, though
further testing might be needed.
Sometimes, a biophysical profile is done, which is when an NST
and ultrasound are performed, looking at the breathing, movement,
amount of amniotic fluid, and tone of the fetus, in addition to the
heart rate response.
Should I Have This Test?
Your health care provider may recommend this if you have a
high-risk pregnancy, if there are concerns during your pregnancy,
or if you have a low-risk pregnancy but are past your due date.
When Should I Have This Test?
An NST may be recommended any time after 26 to 28 weeks,
depending on why it is needed.
How Is the Test Performed?
The health care provider will measure the response of the
fetus' heart rate to each movement the fetus makes as reported
by the mother or observed by the doctor on an ultrasound screen. If
the fetus doesn't move during the test, he or she may be asleep
and the health care provider may use a buzzer to wake the baby. You
also may be asked to drink or eat to try to stimulate the baby
more.
When Are the Results Available?
Immediately.
Contraction Stress Test
Why Is This Test Performed?
This test stimulates the uterus with pitocin, a synthetic form
of oxytocin (a hormone secreted during childbirth), to determine
the effect of contractions on fetal heart rate. It may be
recommended when a nonstress test or biophysical
profile indicates a problem and can determine whether the
baby's heart rate remains stable during contractions.
Should I Have This Test?
This test may be ordered if the nonstress test or
biophysical profile indicates a problem. However, it can induce
labor.
When Should I Have This Test?
Your doctor may schedule it if he or she is concerned about how
the baby will respond to contractions or feels that it is the
appropriate test to determine the fetal heart rate response to a
stimulus.
How Is the Test Performed?
Mild contractions are brought on either by injections of pitocin
or by squeezing the mother's nipples (which causes oxytocin to
be secreted). The fetus' heart rate is then monitored.
When Are the Results Available?
Immediately.
Percutaneous Umbilical Blood Sampling (PUBS)
Why Is This Test Performed?
This test obtains fetal blood by guiding a needle into the
umbilical cord. It's primarily used in addition to an
ultrasound and amniocentesis if your health care provider needs to
quickly check your baby's chromosomes for defects or disorders
or is concerned that your baby may have another problem, such as a
low platelet count or a thyroid condition.
The advantage to this test is its speed. There are situations
(such as when a fetus shows signs of distress) in which it's
helpful to know whether the fetus has a fatal chromosomal defect.
If the fetus is suspected to be anemic or to have a platelet
disorder, this test is the only way to confirm this because it
provides a blood sample rather than amniotic fluid. It also allows
transfusion of blood or needed fluids into the baby while the
needle is in place.
Should I Have This Test?
This test may be used:
- after an abnormality has been noted on an ultrasound
- when results from other tests, such as amniocentesis,
aren't conclusive
- if the fetus may have Rh disease
- if you've been exposed to an infectious disease that
could potentially affect fetal development
Risks are associated with this procedure, such as miscarriage or
infection, so the risks and benefits should be discussed with your
health care provider.
When Should I Have This Test?
After 18 weeks.
How Is the Test Performed?
A fine needle is passed through your abdomen and uterus into the
umbilical cord and blood is withdrawn for testing.
When Are the Results Available?
Usually within 3 days.
Talking to Your Health Care Provider
Some prenatal tests can be stressful, and because many
aren't definitive, even a negative result may not completely
relieve any anxiety you might be experiencing. Because many women
who have abnormal tests end up having healthy babies and because
some of the problems that are detected can't be treated, some
women decide not to have some of the tests.
One important thing to consider is what you'll do in the
event that a birth defect or chromosomal abnormality is discovered.
Your health care provider or a genetic counselor can help you
establish priorities, give you the facts, and discuss your
options.
It's also important to remember that tests are
offered
to women - they are not mandatory. You should feel free to ask your
health care provider why he or she is ordering a certain test, what
the risks and benefits are, and, most important, what the results
will - and won't - tell you.
If you think that your health care provider isn't answering
your questions adequately, you should say so. Things you might want
to ask include:
- How accurate is this test?
- What are you looking to get from these test results?/What do
you hope to learn?
- How long before I get the results?
- Is the procedure painful?
- Is the procedure dangerous to me or the fetus?
- Do the potential benefits outweigh the risks?
- What could happen if I don't undergo this test?
- How much will the test cost?
- Will the test be covered by insurance?
- What do I need to do to prepare?
You also can ask your health care provider for literature about
each type of test.
Preventing Birth Defects
The best thing that mothers-to-be can do to avoid birth defects
and problems with the pregnancy is to
take care
of their bodies by:
- not smoking (and avoiding secondhand smoke)
- avoiding alcohol and other drugs
- checking with the doctor about the safety of prescription and
over-the-counter medications
- avoiding fumes, chemicals, radiation, and excessive heat
- eating a
healthy diet
- taking prenatal vitamins - if possible, beginning before
becoming pregnant
- getting
exercise
(after discussing it with the doctor)
- getting plenty of
rest
- getting
prenatal care
- if possible, beginning with a preconception visit to the doctor
to see if anything needs to change before you get pregnant
Reviewed by:
Larissa Hirsch, MD
Date reviewed: July 2008
Originally reviewed by:
George A. Macones, MD
Note: All information is for educational purposes only. For specific medical advice,
diagnoses, and treatment, consult your doctor.
© 1995-2009 The Nemours Foundation/KidsHealth. All rights reserved.