Common Tests During Pregnancy
The following 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. This screening process can help to determine the risk of the fetus having
certain birth defects. Screening tests may be used alone or with other tests.
There are 3 parts of first trimester screening:
Ultrasound test for fetal nuchal translucency (NT). Nuchal translucency screening uses an ultrasound test to examine the area at the back
of the fetal neck for increased fluid or thickening.
Two maternal serum (blood) tests. The blood tests measure 2 substances found in the blood of all pregnant women:
Pregnancy-associated plasma protein screening (PAPP-A)--a protein produced by the placenta in early pregnancy. Abnormal levels are associated
with an increased risk for chromosome abnormality.
Human chorionic gonadotropin (hCG)--a hormone produced by the placenta in early pregnancy. Abnormal levels are associated
with an increased risk for chromosome abnormality.
When used together as first trimester screening tests, nuchal translucency screening
and maternal blood tests have a greater ability to determine if the fetus might have
a birth defect, such as Down syndrome (trisomy 21) and trisomy 18.
If the results of these first trimester screening tests are abnormal, genetic counseling
is recommended. More testing such as chorionic villus sampling, amniocentesis, cell-free
fetal DNA, or other ultrasounds may be needed for accurate diagnosis.
Second trimester prenatal screening tests
Second trimester prenatal screening may include several blood tests, called multiple
markers. These markers give information about a woman's risk of having a baby with
certain genetic conditions or birth defects. Screening is usually done by taking a
sample of the mother's blood between the 15th and 20th weeks of pregnancy (16th to
18th is ideal). The multiple markers include:
Alpha-fetoprotein screening (AFP). This blood test measures the level of alpha-fetoprotein in the mothers' blood during
pregnancy. AFP is a protein normally produced by the fetal liver and is present in
the fluid surrounding the fetus (amniotic fluid), and crosses the placenta into the
mother's blood. The AFP blood test is also called MSAFP (maternal serum AFP).
Abnormal levels of AFP may signal:
Open neural tube defects (ONTD), such as spina bifida
Other chromosomal abnormalities
Defects in the abdominal wall of the fetus
Twins--more than one fetus is making the protein
A miscalculated due date, as the levels vary throughout pregnancy
hCG. This is human chorionic gonadotropin hormone (a hormone produced by the placenta).
Estriol. This is a hormone produced by the placenta.
Inhibin. This is a hormone produced by the placenta.
Abnormal test results of AFP and other markers may mean more testing is needed. Usually
an ultrasound is done to confirm the dates of the pregnancy and to look at the fetal
spine and other body parts for defects. An amniocentesis may be needed for accurate
Multiple marker screening is not diagnostic. This means it is not 100% accurate, and
is only a screening test to determine who in the population should be offered more
testing for their pregnancy. There can be false-positive results--indicating a problem
when the fetus is actually healthy or false negative results--indicating a normal
result when the fetus actually does have a health problem.
When a woman has both first and second trimester screening tests done, the ability
of the tests to detect an abnormality is greater than using just one screening independently.
Nearly all cases of Down Syndrome can be detected when both first and second trimester
screening are used.
What is an amniocentesis?
An amniocentesis is a procedure used to take a small sample of the amniotic fluid
that surrounds the fetus. It is done to diagnose chromosomal disorders and open neural
tube defects (ONTDs), such as spina bifida. Testing is available for other genetic
defects and disorders depending on the family history and availability of lab testing
at the time of the procedure. An amniocentesis is generally offered to women between
the 15th and 20th weeks of pregnancy who are at increased risk for chromosome abnormalities,
such as women who are over age 35 years of age at delivery, or those who have had
an abnormal maternal serum screening test, indicating an increased risk for a chromosomal
abnormality or neural tube defect.
How is an amniocentesis done?
An amniocentesis involves inserting a long, thin needle through the mother's abdomen
into the amniotic sac to withdraw a small sample of the amniotic fluid for examination.
The amniotic fluid contains cells shed by the fetus, which contain genetic information.
Although specific details of each procedure vary slightly, generally, an amniocentesis
follows this process:
The woman's abdomen is cleansed with an antiseptic.
The doctor may or may not give a local anesthetic to numb the skin.
Ultrasound is used to help guide a hollow needle into the amniotic sac.
A small sample of fluid is withdrawn for lab analysis.
Strenuous activities should be avoided for 24 hours following an amniocentesis.
Women may feel some cramping during or after the amniocentesis.
Women with twins or other multiples need sampling from each amniotic sac, to study
each baby. Depending on the position of the baby, placenta, amount of fluid, or patient's
anatomy, sometimes the amniocentesis cannot be done. The fluid is sent to a genetics
lab so that the cells can grow and be analyzed. Alpha-fetoprotein, a protein made
by the fetus that is present in the fluid, is also measured to rule out an open neural
tube defect, such as spina bifida. Results are usually available in about 10 days
to 2 weeks, depending on the lab.
What is a chorionic villus sampling (CVS)?
Chorionic villus sampling (CVS) is a prenatal test that involves taking a sample of
some of the placental tissue. This tissue contains the same genetic material as the
fetus and can be tested for chromosomal abnormalities and some other genetic problems.
Testing is available for other genetic defects and disorders depending on the family
history and availability of lab testing at the time of the procedure. Unlike amniocentesis
(another type of prenatal test), CVS does not provide information on neural tube defects
such as spina bifida. For this reason, women who undergo CVS also need a follow-up
blood test between 16 to 18 weeks of their pregnancy, to screen for neural tube defects.
How is CVS done?
CVS may be offered to women who are at increased risk for chromosomal abnormalities
or have a family history of a genetic defect that is testable from the placental tissue.
CVS is usually done between the 10th and 13th weeks of pregnancy. Although exact methods
can vary, the procedure involves inserting a small tube called a catheter through
a woman's vagina and into her cervix and usually follows this process:
Ultrasound is used to guide the catheter into place near the placenta.
Tissue is removed using a syringe on the other end of the catheter.
Another method is transabdominal CVS, which involves inserting a needle through the
woman's abdomen and into her uterus to sample the placental cells.
Women may feel some cramping during and after the CVS procedure.
The tissue samples are sent to a genetic lab to grow and be analyzed. Results are
usually available in about 10 days to 2 weeks, depending on the lab.
Women with twins or other multiples usually need sampling from each placenta. However,
because of the complexity of the procedure, and positioning of the placentas, CVS
is not always feasible or successful with multiples.
Some women may not be candidates for CVS or may not get results that are 100% accurate,
and may therefore require a follow-up amniocentesis. In some cases there is an active
vaginal infection, such as herpes or gonorrhea, which will prohibit the procedure.
Other times the doctor takes a sample that does not have enough tissue to grow in
the lab, such that results are incomplete or inconclusive.
What is fetal monitoring?
During late pregnancy and during labor, your doctor may want to monitor the fetal
heart rate and other functions. Fetal heart rate monitoring is a method of checking
the rate and rhythm of the fetal heartbeat. The average fetal heart rate is between
110 and 160 beats per minute. The fetal heart rate 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. An abnormal pattern
also may mean that an emergency or cesarean delivery is needed.
How is fetal monitoring done?
Using a fetoscope (a type of stethoscope) to listen to the fetal heart beat is the
most basic type of fetal heart rate monitoring. 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.
Although the specific details of each procedure vary slightly, generally, electronic
fetal monitoring follows this process:
Gel is applied to the mother's abdomen to act as a medium for the ultrasound transducer.
The ultrasound transducer is attached to the abdomen with straps and transmits the
fetal heartbeat to a recorder. The fetal heart rate is displayed on a screen and printed
onto special paper.
During contractions, an external tocodynamometer (a monitoring device that is placed
over the top of the uterus with a belt) can record the patterns of contractions.
Sometimes, internal fetal monitoring is needed for a more accurate reading of the
fetal heart rate. Your bag of waters (amniotic fluid) must be broken and your cervix
must be partially dilated to use internal monitoring. Internal fetal monitoring involves
inserting an electrode through the dilated cervix and attaching the electrode to the
scalp of the fetus, called a fetal scalp electrode.
What are a glucose challenge and a glucose tolerance tests?
The initial 1-hour test is a glucose challenge test. If the results are abnormal,
a glucose tolerance test is done.
A glucose tolerance test, usually conducted in the 24 to 28 weeks of pregnancy, measures
levels of sugar (glucose) in the mother's blood. Abnormal glucose levels may indicate
How is a glucose tolerance test done?
The glucose tolerance test is done if the woman has an elevated 1-hour glucose challenge
Although the specific details of each procedure vary slightly, generally, a glucose
tolerance test follows this process:
The mother-to-be may be asked to only drink water on the day the glucose tolerance
test is given.
An initial fasting sample of blood is drawn from a vein.
You will be given a special glucose solution to drink.
Blood will be drawn several times over the course of 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
25% of all women. GBS infection usually causes no problems in women before pregnancy,
but can cause serious illness in the mother during pregnancy. GBS may cause chorioamnionitis
(a severe infection of the placental tissues) and postpartum infection. Urinary tract
infections caused by GBS can lead to preterm labor and birth, or pyelonephritis and
GBS is the most common cause of life-threatening infections in newborns, including
pneumonia and meningitis. Newborn babies contract the infection during pregnancy or
from the mother's genital tract during labor and delivery.
The Centers for Disease Control and Prevention recommends screening of all pregnant
women for vaginal and rectal group B strep colonization between 35 to 37 weeks' gestation.
Treatment of mothers with certain risk factors or positive cultures is important to
reduce the risk of transmission of GBS to the baby. Babies whose mothers receive antibiotic
treatment for a positive GBS test are 20 times less likely to develop the disease
than those without treatment.
What is an ultrasound?
An ultrasound scan is a diagnostic technique which uses high-frequency sound
waves to create an image of the internal organs. A screening ultrasound is sometimes
done during the course of a pregnancy to check normal fetal growth and verify the
due date. Ultrasounds may be done at various times throughout pregnancy for different
In the first trimester
To establish the due date -- this is the most accurate way of determining the due
To determine the number of fetuses and identify placental structures
To diagnose an ectopic pregnancy or miscarriage
To examine the uterus and other pelvic anatomy
In some cases to detect fetal abnormalities
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 determine the number of fetuses and examine the placental structures
To assist in prenatal tests, such as an amniocentesis
To examine the fetal anatomy for presence of abnormalities
To check the amount of amniotic fluid
To examine blood flow patterns
To observe fetal behavior and activity
To examine the placenta
To measure the length of the cervix
To monitor fetal growth
To monitor fetal growth
To check the amount of amniotic fluid
As part of the biophysical profile
To determine the position of a fetus
To assess the placenta
How is an ultrasound scan done?
Although the specific details of each procedure vary slightly, generally, ultrasounds
follow this process. Two types of ultrasounds can be done during pregnancy:
In an abdominal ultrasound, gel is applied to the abdomen and the ultrasound transducer
glides over the gel on the abdomen to create the image.
In a transvaginal ultrasound, a smaller ultrasound transducer is inserted into the
vagina and rests against the back of the vagina to create an image. A transvaginal
ultrasound produces a sharper image and is often used in early pregnancy.
There are several types of ultrasound imaging techniques. The most common is 2 dimensional,
or 2D. This gives a flat picture of one aspect of the image.
If more information is needed, a 3D ultrasound exam can be done. This technique, which
provides a three-dimensional picture, requires a special machine and special training.
But the 3D image allows the healthcare provider to see width, height, and depth of
images, which can be helpful in diagnosis. The 3D images can also be captured and
saved for later review.
The latest technology is 4D ultrasound, which allows the healthcare provider to visualize
the unborn baby moving in real-time. With 4D imaging, a 3-dimensional image is continuously
updated, providing a "live action" view. These images often have a golden color, which
helps show shadows and highlights.
Ultrasound images may be captured in still photographs or on video to document findings.
Ultrasound is a technique that is constantly being improved and refined. As with any
test, results may not be completely accurate. However, ultrasound can give valuable
information for parents and healthcare providers to help manage and care for the pregnancy
and fetus. In addition, ultrasound gives parents a unique opportunity to see their
baby before birth, helping 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 due to pressure from
the transducer on the abdomen or in the vagina. No radiation is used during the procedure.
Transvaginal ultrasound requires covering the ultrasound transducer in a plastic or
latex sheath, which may cause a reaction in women with a latex allergy.
Fetal ultrasound is sometimes offered in nonmedical settings to provide keepsake images
or videos for parents. While the ultrasound procedure itself is considered safe, it
is possible that untrained personnel may give parents false assurances about their
baby's well-being, or perhaps an abnormality may be missed. Having ultrasound done
by trained medical personnel who can correctly interpret findings is recommended.
Talk with your doctor or midwife if you have questions.
What is genetic screening?
Many genetic abnormalities can be diagnosed before birth. Your doctor or midwife may
recommend 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 abnormality.
Examples of genetic disorders that can be diagnosed before birth include the following:
What do genetic screening methods include?
Genetic screening methods may include the following:
Alpha-fetoprotein test (AFP) or multiple marker test
Chorionic villus sampling (CVS)
Percutaneous umbilical blood sampling (withdrawing a small sample of the fetal blood
from the umbilical cord)