First Trimester:
Tests and Procedures page 2

FIRST TRIMESTER SCREENING
Introduced in 2004, this relatively new screening can help detect 85% of Down syndrome cases and 97% of Trisomy 18 cases.

What is it?
A blood test and an ultrasound.

When is it performed?
Between weeks 11–14

What does it look for?
The blood test looks for the levels of two proteins, FreeBeta-hCG and PAPP-A. The ultrasound is used to measure the layer of fluid behind the baby’s neck (also called  “nuchal translucency” or a “nuchal fold scan”). By analyzing the results of these two tests, your doctor can assess the likelihood of Down syndrome or Trisomy 18. If the results are abnormal, you can opt for further testing, i.e., CVS or amniocentesis.

Who should have the procedure?
Since these procedures are non-invasive, it is recommended that most pregnant women have the first trimester screening.

Why do it?
When the results from both of these tests are analyzed together, they can be excellent tools in assessing the likelihood of Down syndrome and Trisomy 18.

Why wouldn’t I do it?
As with most prenatal testing, if you are planning on carrying your pregnancy to term regardless of any test results, you would not need to have first trimester screening.

Additional Notes
The American College of Obstetrics and Gynecology notes that “small differences in NT [nuchal translucency] measurements can have a large impact on the risk prediction of Down syndrome.” Additionally, ACOG does not recommend “using the NT measurement by itself to screen for Down syndrome because it has a high positive screen rate when used without serum [from the blood test] markers.”

ULTRASOUND
What is it?
Using high frequency sound waves, a gel is first rubbed on the woman’s belly, and then a transducer is moved across the belly, producing sound waves that bounce off bones and tissue, providing pictures of the baby (a sonogram).

When is it performed?
You might have had an ultrasound at your first visit in order to confirm your pregnancy. If not, you might get a peek at your baby during the nuchal fold scan (listed above in FIRST TRIMESTER SCREENING, usually performed between weeks 11-14. The next ultrasound is scheduled between weeks 16-20, although some doctors – especially if you have a high-risk pregnancy – might check in on your baby’s progress with an ultrasound more frequently.

What does it look for?
Through an ultrasound, your doctor can check the fetal heartbeat as well as measure your baby to establish gestational age and monitor how your baby is growing. An ultrasound also gives your doctor a firsthand look at any potential problems, i.e., spina bifida or placenta previa.

Who should have the procedure?
Most pregnant women can benefit from an ultrasound at some point in their pregnancy.