Common Tests During Pregnancy

Common Tests During Pregnancy

These are some of the more common tests done during pregnancy.

First trimester prenatal screening tests

First trimester screening is a combination of fetal ultrasound and maternal blood
testing. It can help find out the risk that the fetus has certain birth defects. Screening
tests may be used alone or with other tests.

First trimester screening has 3 parts.

Ultrasound test for fetal nuchal translucency (NT)

Nuchal translucency screening uses an ultrasound test to check the area at the back
of the fetal neck for extra fluid or thickening.

Two maternal serum (blood) tests

These tests measure 2 substances found in the blood of all pregnant women: 

  • Pregnancy-associated plasma protein screening (PAPP-A). This is a
    protein made by the placenta in early pregnancy. Abnormal levels are linked to
    a higher risk for chromosome problems.

  • Human chorionic gonadotropin (hCG). This is a hormone made by the
    placenta in early pregnancy. Abnormal levels are linked to a higher risk for
    chromosome problems.

When used together, these tests have a greater ability to find out if the fetus might
have a genetic birth defect such as Down syndrome (trisomy 21) and trisomy 18.

If the results of these tests are abnormal, your healthcare provider will suggest
genetic counseling. You may need more testing. That may include chorionic villus sampling,
amniocentesis, cell-free fetal DNA, or other ultrasounds.

Second trimester prenatal screening tests

Second trimester prenatal screening may include several blood tests. These are called
multiple markers. They give information about a woman’s risk of having a baby with
certain genetic conditions or birth defects. Screening is often done by taking a sample
of your blood between the 15th and 20th weeks of pregnancy. The 16th to 18th is ideal.
The multiple markers are listed below.

Alpha-fetoprotein screening (AFP)

This blood test measures the
level of alpha-fetoprotein in your blood during pregnancy. AFP is a protein normally
made by the fetal liver. It is in the fluid around the fetus (amniotic fluid) and
crosses the placenta into your blood. The AFP blood test is also called MSAFP
(maternal serum AFP). Abnormal levels of AFP may be a sign of:

  • Open neural tube defects (ONTD) such as spina bifida

  • Down syndrome

  • Other chromosome problems

  • Problems in the abdominal wall of the fetus

  • Twins. More than one fetus is making the protein.

  • An incorrect due date. The levels of AFP vary throughout pregnancy.

Other markers

Other markers are:

  • hCG. This is human chorionic gonadotropin hormone. It is made by the
    placenta.

  • Estriol. This is a hormone made by the placenta.

  • Inhibin. This is a hormone made by the placenta.

Abnormal results of AFP and other markers may mean you need more testing. An ultrasound
is often done to confirm the dates of the pregnancy. It also looks at the fetal spine
and other body parts for problems. You may need an amniocentesis for accurate diagnosis.

Multiple marker screening is not diagnostic. This means it is not 100% accurate. It
is only a screening test to find out who should be offered more testing for their
pregnancy. The tests show false-positive results. This means they show a problem when
the fetus is actually healthy. Or the results may be false negative. This means they
show that the fetus is normal when the fetus actually does have a health problem.

Having both first and second
trimester screening tests done makes it more likely to find a problem, if there is
one, than using just one screening alone. As many as 19 out of 20 cases of Down
syndrome can be found when both first and second trimester screening are used.

What is an amniocentesis?

An amniocentesis is a test that takes a small sample of the amniotic fluid. It is
done to diagnose chromosome problems and open neural tube defects (ONTDs) such as
spina bifida. The test can also look for other genetic problems and disorders if you
have a family history of them. These other results also depend on the lab doing the
testing. An amniocentesis is generally offered to women between the 15th and 20th
weeks of pregnancy who are at higher risk for chromosome problems. This includes women
who have had an abnormal maternal blood screening test. The test may have indicated
a higher risk for a chromosome problem or neural tube defect.


Illustration demonstrating  an  amniocentesis

How is an amniocentesis done?

An amniocentesis involves putting a
long, thin needle through your abdomen into the amniotic sac. The healthcare provider
withdraws a small sample of the amniotic fluid. The amniotic fluid has cells shed
by the
fetus. These cells have genetic information. The specific details of each test vary
slightly, but an amniocentesis often follows this process:

  • The healthcare team cleans your belly (abdomen) with an antiseptic.

  • The healthcare provider may use a local anesthetic to numb the skin.

  • The provider uses ultrasound to help guide a hollow needle into the amniotic sac.

  • The provider withdraws a small sample of fluid to be sent to a lab.

After the test, don’t do any strenuous activity for 24 hours. You may feel some cramping
during or after the amniocentesis.

If you are carrying twins or other
multiples, you will need sampling from each amniotic sac to study each baby.

The fluid sample is sent to a genetics lab so that the cells can grow and be tested.
AFP is also measured to rule out an open neural tube defect such as spina bifida.
AFP is a protein made by the fetus and is in the fluid.

Results are often available in 10 days to 2 weeks, depending on the lab.

Discuss the risks of this procedure with your healthcare provider. Sometimes the amniocentesis
can’t be done. It depends on the position of the baby, the placenta, the amount of
fluid, and your anatomy.

What is a chorionic villus sampling (CVS)?

Chorionic villus sampling (CVS) is a prenatal test. It involves taking a sample of
some of the placental tissue. This tissue often has the same genetic material as the
fetus. It can be tested for chromosome problems and some other genetic problems. The
test can also look for other genetic problems and disorders if you have a family history
of them. These other results also depend on the lab doing the testing. Unlike amniocentesis,
CVS does not give information on neural tube defects such as spina bifida. For this
reason, women who have CVS also need a follow-up blood test between 16 and 18 weeks
of their pregnancy to screen for neural tube defects.


Illustration demonstrating  a  transcervical chorionic villus sampling

How is CVS done?

CVS may be offered if you are at
higher risk for chromosome problems. You may also be offered it if you have a family
history of a genetic problem that is testable from the placental tissue. CVS is usually
done between the 10th and 13th weeks of pregnancy. The exact method for CVS can vary,
but the procedure involves putting a small tube (catheter) through your vagina and
into
your cervix. It usually follows this process:

  • The healthcare provider uses ultrasound to guide the catheter into place near the
    placenta.

  • The provider removes tissue using a syringe on the other end of the catheter.

  • For a transabdominal CVS, the provider puts a needle through your abdomen and into
    the uterus to take a sample of cells from the placenta.

  • You may feel some cramping during and after the CVS procedure.

If you are carrying twins or other
multiples, you often will need sampling from each placenta. But CVS is not always
advised for multiples because the procedure is complicated and the placentas may not
be
in a good position to get a sample.

The tissue samples are sent to a genetic lab to grow and be tested. Results are often
available in 10 days to 2 weeks, depending on the lab.

Some women may not be candidates
for CVS, or they may not get results that are 100% accurate. They may need a follow-up
amniocentesis. In some cases, an active vaginal infection such as herpes or gonorrhea
will prohibit the procedure. Other times, the healthcare provider takes a sample that
does not have enough tissue to grow in the lab. That may cause incomplete or
inconclusive results.

Discuss the risks of CVS with your healthcare provider.

What is fetal monitoring?

During late pregnancy and during labor, your healthcare provider may want to watch
the fetal heart rate and other functions. Fetal heart rate monitoring is a way of
checking the rate and rhythm of the fetal heartbeat. The average fetal heart rate
is between 110 and 160 beats per minute. It may change as the fetus responds to conditions
in the uterus. An abnormal fetal heart rate or pattern may mean that the fetus is
not getting enough oxygen or there are other problems. It also may mean that an emergency
or cesarean delivery is needed.

How is fetal monitoring done?

The most basic type of fetal heart rate monitor is to use a type of stethoscope called a
fetoscope. Another type of monitoring is with a hand-held Doppler device. This is
often used during prenatal visits to count the fetal heart rate. During labor, continuous
electronic fetal monitoring is often used. The specific details may vary slightly,
but electronic fetal monitoring often follows this process:

  • The healthcare provider puts gel on your abdomen to help the ultrasound transducer
    work properly.

  • The provider attaches the ultrasound transducer to the abdomen with straps and sends
    the fetal heartbeat to a recorder. The fetal heart rate is displayed on a screen and may
    be printed onto special paper.

  • During contractions, a monitoring device (external tocodynamometer) is placed over
    the top of the uterus with a belt. This device can record the patterns of contractions.

Sometimes, internal fetal
monitoring is needed for a more accurate reading of the fetal heart rate. This
monitoring can be done when birth is close. Your amniotic sac must be broken, and
your
cervix must be partially dilated to do it. Internal fetal monitoring involves putting
an
electrode through the dilated cervix. The electrode is attached to the scalp of the
fetus.

What are glucose tolerance tests and the
glucose challenge?

The first 1-hour test is a glucose challenge test. If the results are abnormal, a
glucose tolerance test is done.

A glucose tolerance test is often done in weeks 24 to 28 of pregnancy. It measures
levels of sugar (glucose) in your blood. Abnormal glucose levels may be a sign of
gestational diabetes.

How is a glucose tolerance test done?

The glucose tolerance test is done if you have an elevated 1-hour glucose challenge
test.

The specific details may vary slightly, but a glucose tolerance test often follows
this process:

  • You may be asked to drink only water on the day you get the test.

  • The healthcare provider will draw a fasting sample of blood from a vein.

  • You will be given a special glucose solution to drink.

  • The provider will draw blood several times over several hours to measure the glucose
    levels in your body.

What is a group B strep culture?

Group B streptococcus (GBS) are bacteria found in the lower genital tract of about
1 in 4 women. GBS infection often causes no problems in women before pregnancy. But
it can cause serious illness in the mother during pregnancy. GBS may cause chorioamnionitis.
This is a severe infection of the placental tissues. It can also cause postpartum
infection. Urinary tract infections caused by GBS can lead to preterm labor and birth,
or pyelonephritis and sepsis.

GBS is the most common cause of life-threatening infections in newborns, including
pneumonia and meningitis. Newborn babies get the infection during pregnancy or from
the mother’s genital tract during labor and birth.

The CDC advises that all pregnant women be screened for vaginal and rectal group B
strep between 35 to 37 weeks gestation. If you have certain risk factors or a positive
result, you should be treated with antibiotics. This will lower the risk of passing
GBS to your baby. Babies whose mothers get antibiotics for a positive GBS test are
20 times less likely to develop the disease than those whose mothers don’t get treatment.

What is an ultrasound?

An ultrasound scan is a test that uses high-frequency sound waves to make pictures
of the internal organs. A screening ultrasound is sometimes done during a pregnancy
to check normal fetal growth and make sure of the due date. Ultrasounds may be done
at various times throughout pregnancy for many reasons.

In the first trimester

  • To find out the due date. This is the most accurate way of finding the due date.

  • To find out the number of
    fetuses and see the placenta(s)

  • To diagnose an ectopic pregnancy or miscarriage

  • To look at the uterus and other pelvic anatomy

  • In some cases to find fetal problems

Mid-trimester (sometimes called the 18- to 20-week scan)

  • To confirm the due date. A due date set in the first trimester is rarely changed.

  • To find out the number of fetuses and look at the placentas

  • To help with prenatal tests such as an amniocentesis

  • To look at the fetal anatomy to see if there are any problems

  • To check the amount of amniotic fluid

  • To look at blood flow patterns

  • To watch fetal behavior and activity

  • To look at the placenta

  • To measure the length of the cervix

  • To check fetal growth

Third trimester

  • To check fetal growth

  • To check the amount of amniotic fluid

  • To complete a biophysical profile

  • To find out the position of a fetus

  • To check the placenta

How is an ultrasound scan done?

The specific details may vary slightly, but ultrasounds often follow the same process.
Two types of ultrasounds can be done during pregnancy:

  • Abdominal ultrasound. In an abdominal ultrasound, the healthcare provider
    puts gel on your abdomen. The ultrasound transducer glides over the gel to create
    the image.

  • Transvaginal ultrasound. In a transvaginal ultrasound, the provider uses
    a smaller ultrasound transducer. They put the transducer into the vagina and rest
    it against the back of the vagina to create an image. A transvaginal ultrasound
    makes a sharper image. It is often used in early pregnancy.

There are several types of
ultrasound imaging techniques. The most common is 2-D. This gives a flat picture of
one
aspect of the image.

If more information is needed, a
3-D ultrasound exam can be done. This technique gives a 3-D picture. It requires a
special machine and special training. But the 3-D image lets the healthcare provider
see
width, height, and depth of images. These can be helpful in diagnosis. The 3-D images
can also be saved for later review.

The latest technology is 4-D
ultrasound. It lets the healthcare provider see the fetus moving in real time. With
4-D
imaging, a 3-D image is continuously updated. This makes a “live action” view. These
images often have a golden color that helps show shadows and highlights.

Ultrasound images may be captured in still photographs or on video to document findings.

Ultrasounds are constantly being improved and refined. As with any test, results may
not be completely accurate. But ultrasound can give valuable information for parents
and healthcare providers to help manage and care for the pregnancy and fetus. Ultrasound
also gives parents a special chance to see their baby before birth. This helps them
to bond and establish an early relationship.

What are the risks and benefits of ultrasound?

Fetal ultrasound has no known risks other than mild discomfort. This is because of
pressure from the transducer on the abdomen or in the vagina. No radiation is used
during the procedure.

Transvaginal ultrasound requires that the ultrasound transducer be covered in a plastic
or latex sheath. This may cause a reaction in women with a latex allergy.

Fetal ultrasound is sometimes offered in nonmedical settings to give keepsake images
or videos for parents. The ultrasound procedure itself is considered safe, but it’s
possible that untrained workers may give parents false assurances about their baby’s
well-being. Or perhaps a problem may be missed. Having ultrasound done by trained
medical staff who can correctly understand findings is recommended. Talk with your
healthcare provider or midwife if you have questions.

What is genetic carrier screening?

Many genetic problems can be diagnosed before birth. Your healthcare provider or midwife
may advise genetic testing during the pregnancy if you or your partner have a family
history of genetic disorders or you have had a fetus or baby with a genetic problem.

Examples of genetic disorders that are commonly screened for include:

  • Cystic fibrosis

  • Spinal muscular dystrophy

  • Fragile X

  • Thalassemia

  • Sickle cell anemia

  • Tay-Sachs disease