• Genetic Screening

• First Trimester 

• Ultrasound

• Amniocentesis

• Chorionic Villus Sampling

• Fetal Monitoring

• Glucose

• Group B Strep Culture

Your health care provider may recommend a variety of screenings, tests and imaging techniques during your pregnancy. These tests are designed to provide information about the health of your baby and may help you optimize your child’s prenatal care and development.

Genetic Screening

Many genetic abnormalities can be diagnosed before birth. Your doctor or midwife may recommend genetic testing during pregnancy if you or your partner has a family history of genetic disorders. You may also choose to have genetic screening if you have had a fetus or baby with a genetic abnormality.

Examples of genetic disorders that can be diagnosed before birth include:

• Cystic fibrosis

• Duchenne muscular dystrophy

• Hemophilia A

• Polycystic kidney disease

• Sickle cell disease

• Spinal Muscular Atrophy 

• Tay-Sachs disease

• Thalassemia

The following screening methods are available during pregnancy:

• Alpha-fetoprotein (AFP) test or multiple marker test

• Amniocentesis

• Chorionic villus sampling

• Cell-free fetal DNA testing

• Percutaneous umbilical blood sampling (withdrawing a small sample of the fetal blood from the umbilical cord)

• Ultrasound scan

First Trimester Prenatal Screening Tests

First trimester screening is a fetal ultrasound and/or maternal blood testing. This screening process can help determine the risk of the fetus having certain birth defects. Screening tests may be used alone or with other tests.

First trimester screening includes:

• Ultrasound for fetal nuchal translucency. Nuchal translucency screening uses an ultrasound to examine the area at the back of the fetal neck for increased fluid or thickening.
• Ultrasound for fetal nasal bone determination. The nasal bone may not be visualized in some babies with certain chromosome abnormalities, such as Down syndrome. This screen is performed using an ultrasound between 11 and 13 weeks gestation.
• Maternal serum (blood) tests:
  • cfDNA for aneuploidy: A maternal blood test that evaluates the relative levels of DNA in the maternal blood to evaluate for trisomy 21, trisomy 18, trisomy 13 and sex chromosome abnormalities.
  • Analyte testing: Measures two substances found in the blood of all pregnant women: pregnancy-associated plasma protein A and human chorionic gonadotropin. Abnormal levels of these proteins are associated with an increased risk of chromosomal abnormality.

If the results of these first trimester screening tests are abnormal, genetic counseling is recommended. Additional testing, such as chorionic villus sampling, amniocentesis, or other ultrasounds, may be needed for an accurate diagnosis.

Ultrasound

An ultrasound scan is a diagnostic technique that uses high-frequency sound waves to create an image of the internal organs. A screening ultrasound is sometimes done during the course of your pregnancy to check normal fetal growth and verify the due date.

When are ultrasounds performed during pregnancy?

Ultrasounds may be done at various times throughout pregnancy for several reasons:

First Trimester

• To establish the due date (this is the most accurate way of determining the due date)

• 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

• To detect fetal abnormalities (in some cases)

Midtrimester (also 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 abnormalities

• To check the amount of amniotic fluid

• To examine blood flow patterns

• To observe fetal behavior and activity

• To measure the length of the cervix

• To monitor fetal growth

Third Trimester

• To monitor fetal growth

• To check the amount of amniotic fluid

• To conduct the biophysical profile test

• To determine the position of the fetus

• To assess the placenta

How is an ultrasound scan performed?

Two types of ultrasounds can be performed during pregnancy:

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

• Transvaginal ultrasound. In a transvaginal ultrasound, a smaller ultrasound transducer is inserted into your vagina and rests against the back of the vagina to create an image. A transvaginal ultrasound produces a sharper image than an abdominal ultrasound and is often used in early pregnancy.

Which ultrasound imaging techniques are available?

There are several types of ultrasound imaging techniques. As the most common type, the 2-D ultrasound provides a flat picture of one aspect of the baby.

If more information is needed, a 3-D ultrasound exam can be done. This technique, which provides a 3-D picture, requires a special machine and special training. The 3-D image allows the health care provider to see the width, height and depth of the images, which can be helpful during the diagnosis. The 3-D images can also be captured and saved for later review.

The latest technology is 4-D ultrasound, which allows the health care provider to visualize the unborn baby moving in real time. With 4-D imaging, a three-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.

What are the risks and benefits of ultrasound imaging?

Fetal ultrasound has no known risks other than mild discomfort due to pressure from the transducer on your abdomen or in your 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.

Ultrasound imaging is constantly being improved and refined. As with any test, the results may not be completely accurate. However, an ultrasound can provide valuable information to parents and health care providers, helping them manage and care for the pregnancy and the baby. In addition, ultrasound imaging gives parents a unique opportunity to see their baby before birth, helping them to bond and establish an early relationship.

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 miss an abnormality or give parents false assurances about their baby’s well-being. It is best to have an ultrasound performed by trained medical personnel who can correctly interpret the results. Talk with your doctor or midwife if you have questions.

Amniocentesis

An amniocentesis involves taking a small sample of the amniotic fluid that surrounds the fetus. It is used to diagnose chromosomal disorders and open neural tube defects, such as spina bifida. Testing is available for other genetic defects and disorders depending on your family history and the availability of lab testing at the time of the procedure.

An amniocentesis is generally offered to women between the 15th and 20th week of pregnancy who have an increased risk of chromosomal abnormalities. Candidates include women who will be over age 35 at the time of delivery or those who have had an abnormal maternal serum screening test. 

Chorionic Villus Sampling (CVS) 

Chronic villus sampling 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 your family history and the availability of lab testing at the time of the procedure.

Unlike amniocentesis, CVS does not provide information on open neural tube defects. Therefore, women who undergo CVS also need a follow-up blood test between 16 and 18 weeks of pregnancy to screen for these defects. 

Women with twins or other higher-order multiples usually need sampling from each placenta. However, because of the complexity of the procedure and the positioning of the placentas, CVS is not always feasible or successful with multiples. Women who are not candidates for CVS or who did not get accurate results from the procedure may require a follow-up amniocentesis. An active vaginal infection, such as herpes or gonorrhea, will prohibit the procedure. In other cases, the doctor may take a sample that does not have enough tissue to grow in the lab, generating incomplete or inconclusive results.

Fetal Monitoring

During late pregnancy and 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 120 and 160 beats per minute. This 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 indicate other problems. An abnormal pattern also may mean that an emergency cesarean delivery is needed.. 

On occasion, internal fetal monitoring is needed to provide 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.

Glucose Testing

Glucose testing is used to measure the level of sugar in your blood. The initial one-hour test is a glucose challenge test. A glucose challenge test is usually conducted between 24 and 28 weeks of pregnancy. If the results are abnormal, a glucose tolerance test is needed. Abnormal glucose levels may indicate gestational diabetes. 

How is a glucose tolerance test performed?

You may be asked to only drink water on the day the glucose tolerance test is given. Although the specific details of each procedure may vary, a typical glucose tolerance test includes the following steps:

• An initial fasting sample of blood will be drawn from your vein.

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

• Blood will be drawn at various times over the course of several hours to measure the glucose levels in your body.

Group B Strep Culture

Group B streptococcus (GBS) is a type of bacteria found in the lower genital tract of about 20 percent of all women. While a GBS infection does not usually cause problems in women before pregnancy, it can cause serious illness in mothers 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 sepsis.

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 all pregnant women for vaginal and rectal GBS colonization between 35 and 37 weeks gestation. The 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.

Medically reviewed by Angie Jelin, M.D., January 23, 2026.