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Prenatal screening tests

​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​Screening tests are used to check if your baby is at risk for certain birth defects.

If a screening test shows an increased risk, further tests may be used to diagnose the problem. An abnormal result, while alarming, only means there is a possible problem.

In most cases, the baby is healthy even if there is an abnormal screening test result. At the same time, a birth defect can occur even if the screen does not show a problem.

Not all problems can be found by testing. Your doctor/ midwife or a genetic counselor can explain the screening test results and what they mean.

Family history

​Family history is one way to find out if your baby is at risk for birth defects.

If you or your partner has a family history of birth defects, multiple miscarriages, stillbirths, or other genetic disorders, there may be an increased risk for your baby.

Carrier screening

Carrier screening is used to check for birth defects that may be inherited. Just as a baby gets certain traits (like eye color) from the parents, some diseases and disorders can also be passed on to the baby.

A carrier is a person who shows no signs of a particular disorder but could pass the gene on to his or her children.

Carrier testing can check for a number of genetic disorders such as cystic fibrosis, sickle cell anemia, Tay-Sachs disease, and Thalassemia.

​Ultrasound

A detailed ultrasound exam is used to view your baby’s organs and features. Ultrasound can also show how your baby is growing.

There is no risk of losing a pregnancy from doing an ultrasound.

A detailed ultrasound exam can find many birth defects, but it cannot diagnose Down syndrome or other chromosome problems.

If ultrasound shows certain types of birth defects or other signs (called “soft markers”), it may raise concerns about a possible genetic condition.

Your health care provider or genetic counselor may talk with you about further diagnostic testing that may help diagnose or rule out certain genetic disorders. ​

When it is usually done:​18-20 weeks

How long it takes to get results:1-2 hours

Test or screen looks for (Accuracy rate):Down Syndrome (up to 60-70%); Trisomny 18 (up to 90%); Open Spina Bifida (up to 90%); Other birth defects

Considerations:

  • No miscarriage risk
  • Assess fetal growth and development
  • Uncertain findings
  • May help decide about AFP4 screen or amniocentesis

First trimester screening

First trimester screening includes a careful look at the baby by using an ultrasound and blood tests.

The ultrasound includes a measurement of the thickness of skin at the back of the baby’s neck. This screening can be done between 11 and 14 weeks of pregnancy.

The screening checks for signs of Down syndrome, and Trisomy 13/18. If the results show there is an increased chance of Down syndrome or Trisomy 13/18, diagnostic testing (chorionic villus sampling or amniocentesis) will be offered.

Diagnostic testing is used to confirm if the baby really has a problem.

First trimester screening cannot check for open spina bifida. To detect open spina bifida it is still necessary to do AFP1 (alpha-fetoprotein) testing in the second trimester (between 15 to 20 weeks). A detailed ultrasound may also be used in the second trimester (usually around 18 to 20 weeks) to look at the baby’s spine.

Name of test or screen:First Trimester Screen

When it is usually done:11-13 weeks

How long it takes to get results:4-7 days

Test or screen looks for (Accuracy rate):Down Syndrome (up to 80-90%); Trisomy 13/18 (90%)

Considerations:

  • No miscarriage risk
  • Early results
  • May help decide about CVS or amniocentesis
  • Not diagnostic – uncertain findings

Name of test or screen:Alpha-fetoprotein Screen (AFPT)

When it is usually done:15-20 weeks

How long it takes to get results:2-3 days

Test or screen looks for (Accuracy rate):Open spina bifida (75%)

Considerations:

  • No miscarriage risk
  • May help decide on amniocentesis
  • Not diagnostic – uncertain findings

Maternal serum screening/Quad screen

This screen checks your blood for any signs that your baby may have Down syndrome, Trisomy 18, or open spina bifida.

These tests are usually done around 15 to 20 weeks of pregnancy. The timing of the test is important because some problems can only be found at a certain point in pregnancy. For example, a high alpha-fetoprotein level can mean you are further along in your pregnancy than you thought, or that you are carrying more than one baby.

If your results are not in the normal range, your doctor/midwife will offer you further testing. In some cases, abnormal levels can be explained with an ultrasound exam.

Name of test or screen:Quad Screen (AFP4)

When it is usually done:15-20 weeks

How long it takes to get results:2-4 days

Test or screen looks for (Accuracy rate):Down Syndrome (80%); Trisomy 18 (60%); Open spina bifida (75%)

Considerations:

  • No miscarriage risk
  • May help decide on amniocentesis
  • Not diagnostic – uncertain findings