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Prenatal Testing

Prenatal tests, which include genetic or DNA testing and ultrasound imaging, can provide valuable insights regarding your health and your baby’s health. Doctors perform some of these tests prior to pregnancy, and others are done during pregnancy.  In some cases, these indicate the need for treatment that could save the life of your unborn child.

Reasons for prenatal testing

  • Identifying health problems in the mother (and sometimes father) that may affect the baby
  • Assessing the baby to determine size, sex, age and placement in uterus
  • Determining the likelihood that the baby has certain congenital, genetic or chromosomal problems
  • Diagnosing fetal abnormalities, such as heart defects

Tests to consider before getting pregnant

Many existing conditions that could be problematic for you and your baby during pregnancy can be treated and very often cured. That’s why it’s a good idea to schedule an appointment with your OB-GYN before becoming pregnant.

Your doctor will discuss your medical history and what tests might be right for you. This could include blood tests for both partners to check for the following:

  • Hepatitis B, sexually transmitted disease (STD) and HIV
  • Immunity to rubella (German measles)
  • Genetic factors that could lead to diseases such as these in children born to you and your partner:
    • Cystic fibrosis
    • Tay-Sach’s disease (in those of Eastern European Jewish descent)
    • Sickle cell anemia (in those of African-American  and Mediterranean descent)
    • Fragile X

Women should also undergo a Pap smear to test for cervical cancer. Pap smears can also be used to detect chlamydia and gonorrhea.

What kinds of tests can you expect during your first prenatal visit?

If you didn’t undergo the tests noted above during pregnancy, you can expect them during your first prenatal visit. And, in some cases, they may be repeated.

In addition, you will undergo blood tests to check for the following:

  • Your blood type and Rh (or rhesus) factor. This protein substance is found in the blood of 85 percent of the population. If you have the protein, you are considered Rh positive; if you don’t, you are Rh negative.

If the mother is Rh negative and the child is Rh positive, the mother must be treated to avoid problems in the baby. Potential problems include anemia, brain damage and even death.

If doctors suspect the baby’s Rh factor is positive, shots of Rh immunoblobulin (e.g., Rhogam) are administered at 28 weeks’ gestation.

  • Anemia. Women who remain anemic during their first two trimesters are at a higher risk of preterm delivery or having a low birth weight baby. Anemia can be treated with dietary supplements.

The doctor or nurse will also do the following at your first visit and subsequent visits:

  • Use fetal Doppler equipment to listen to the baby’s heartbeat.
  • Administer a urine test, which will determine if you have a urinary tract infection.

A glucose tolerance test (see below) may be performed early and also later in pregnancy for the following reasons:

  • You previously had gestational diabetes
  • You are obese
  • You have had a child weighing more than 9 pounds
  • You have a family history of diabetes
  • You meet other criteria established by your physician

What kinds of tests can you expect later in pregnancy?

  • Urine test (performed at every visit) to evaluate glucose and protein levels, which could be indicators of gestational diabetes.
  • Glucose tolerance test (performed between 24 and 28 weeks’ gestation) to check for gestational diabetes. This involves drinking a very sweet substance, waiting an hour and then having blood drawn.
  • Group B streptococcus screening is performed between 35 and 36 weeks’ gestation. This test is done to see if you have bacteria that, if left untreated, could prove harmful to your baby. The screening is performed by swabbing cells from the lower end of the vagina and rectum. If you test positive, antibiotics will be given to you during labor.
  • Ultrasound tests are performed between eight and 20 weeks’ gestation; the frequency can vary.  These tests are done for several reasons:
    • See if the baby is growing normally
    • Verify expected delivery date
    • Assess amount of amniotic fluid and indicate position of placenta (this occurs later in the second and third trimesters)
    • Screen for some potential birth defects
  • Level II ultrasounds (including 3D and 4D ultrasounds) are often performed if the expectant mother has risk factors (e.g., advanced maternal age for having a child with a birth defect). These ultrasounds provide more detailed information and can help detect the following:
    • Cleft lip
    • Birth defects of the hands and feet, brain, spine, heart, kidneys or other organs
  • Cervical measurement (between 16 and 20 weeks’ gestation) via ultrasound can help doctors determine if a woman is at risk for preterm delivery. If the findings indicate it is likely, doctors may recommend medication, minor surgery or behavior changes (e.g., no rigorous exercise). 

What kinds of tests are done if you are over 35 and pregnant or have genetic concerns?

If you are 35 or older or have genetic concerns, your doctor may recommend additional tests.

Screening tests for genetic concerns

Screening tests do not provide definitive answers. Instead, they indicate the likelihood that a child will be born with certain genetic disorders, such as Down syndrome, trisomy 18 and trisomy 13. Some of these tests are available regardless of age or risk factors If a screening test indicates a problem, diagnostic testing is usually recommended.

  • First trimester screening test: This test involves a blood test to measure the levels of two key proteins found in pregnant women and ultrasound to measure skin thickness behind the neck of the fetus (nuchal translucency). 
  • Quad screen, also called maternal serum screening (typically done between 15 and 20 weeks’ gestation): This blood test evaluates four components of a pregnant woman’s blood.
  • Integrated screen: This test combines components of the first trimester screen with the quad screen to provide a more complete picture than one screen can provide.
  • Free fetal DNA test: This blood test is more predictive of fetal genetic abnormalities than the other tests listed above because it detects small amounts of the fetal DNA in a simple blood sample from the mother.

Diagnostic tests for genetic disorders

Diagnostic tests provide definitive answers regarding many genetic disorders, including Down syndrome, cystic fibrosis and Huntington’s disease

  • Chorionic villus sampling (CVS) can, with almost 100 percent certainty, indicate whether a baby has or does not have Down syndrome. CVS is performed early in pregnancy between 11 and 13 weeks’ gestation.

In most cases, doctors insert a thin tube through a woman’s vagina and cervix using ultrasound guidance and remove a small sample of tissue, which is then sent to a lab for evaluation. Risks include miscarriage (between 1 in 200 and 1 in 100 women miscarry after CVS). 

  • Amniocentesis indicates whether or not a baby has Down syndrome, spina bifida and anencephaly but it can’t be performed until the second trimester. Like CVS, its results are almost always correct.

Using ultrasound to guide them, doctors insert a needle into the sac surrounding the baby and remove amniotic fluids for evaluation. For most women, discomfort is minimal.

Risks include miscarriage (1 in 300) and loss of amniotic fluid. Loss of fluid resolves itself in most cases but can cause complications such as infection, preterm delivery and possible pregnancy loss.

Other tests for genetic disorders

  • Fetal echocardiography: Doctors use this test to evaluate a baby’s heart prior to birth. Like an ultrasound, the test uses sound waves.
  • Percutaneous umbilical blood sampling (cordocentesis): In this test, a sample of the baby’s blood is taken from the umbilical cord. This can test to see if the baby has anemia or an infection, Down syndrome or other abnormal chromosomes. It can also be used to deliver blood transfusions or medications to the baby.

Why choose Rush for prenatal testing

  • OB-GYNs and maternal-fetal medicine specialists offer all of these prenatal tests.
  • The Fetal and Neonatal Medicine Program at Rush brings together multiple specialists to meet with expectant families who have concerns about their unborn baby’s health. They provide medical expertise as well as map out treatment plan for pregnant women and their babies. They also offer valuable second opinions so you can make the most informed decisions possible.
  • At Rush, you will find genetic specialists who can identify your risks of passing on genetic conditions to your children. They offer counseling to families before and during pregnancy.
  • Maternal-fetal medicine doctors at Rush specialize in caring for women with gestational diabetes, anemia and other condition. These doctors are fellowship trained in treating women facing high-risk pregnancies.
  • The new Rush Family Birth Center was designed to address the unique needs of women facing high-risk pregnancies and their babies. It has dedicated rooms for high-risk pregnant women who are awaiting delivery of their babies.
  • Part of the Rush Family Birth Center, the level III neonatal intensive care unit (NICU) is strategically located next to labor and delivery. This proximity helps at-risk babies get the care they need immediately after delivery.