What are Screening Tests and What Types Are Available?
Screening tests have been designed to identify women who are at an increased risk of having babies with certain chromosomal abnormalities like Down syndrome, selected inherited diseases like cystic fibrosis or thalassemia, or physical birth defects like spina bifida. These tests pose no risk to the pregnancy and identify many but not all women who are carrying fetuses affected with the conditions that are being screened.
There are a series of individual markers used to identify women carrying fetuses likely to be affected with Down syndrome or other problems. Screening tests are used to adjust your risk based on your age. Proteins in a pregnant woman’s blood and/or ultrasound can be combined in various ways to assess the risk for Down syndrome. Each test has specific benefits and your genetic counselor will help you decide which test, if any, may be right for your pregnancy. All of these screening tests are non-invasive, with no increased risk for miscarriage. Individual tests offered at our center include:
First Trimester Screen
Also known as the combined screen, this screening test is the earliest offered in pregnancy. Between 11 and 14 weeks gestation, our nurse draws your blood to evaluate two proteins. You will also have a specialized ultrasound, called a Nuchal Transulcency (NT) performed at this time. The NT screening is a high-resolution ultrasound used to measure the amount of fluid underneath the skin at the back of the fetus’ neck. It is performed exclusively by physicians and sonographers who have special certification to perform this test. The main benefit of the First Trimester Screen is that it offers the earliest screen results for Down syndrome and trisomy 18. This test does not screen for spina bifida and other neural tube defects. Results are available approximately one week after the ultrasound and blood work are performed.
Read Genzyme's patient brochure (pdf file) on First Trimester Screen.
Integrated Screen
Integrated Screen is a screening test that looks at both first and second trimester markers to assess the risk for Down syndrome and trisomy 18. This test also assesses the chance for open neural tube defects, such as spina bifida in a pregnancy. Integrated screening consists of two phases:
- The first phase, like the First Trimester Screen, is performed at our center at 11-14 weeks of pregnancy. The specialized NT ultrasound is used to measure the amount of fluid underneath the skin at the back of the fetus’ neck. Also, the mother’s blood is drawn at this time.
- The second phase consists of an additional blood test, performed at 15-20 weeks of pregnancy.
Approximately one week after the second blood sample is drawn, the results are available. The main benefit of the Integrated Screen is that it offers the highest detection rate for Down syndrome of all the screening tests.
These screening tests are options available at the Prenatal Diagnosis Center. They are offered as alternatives to the Expanded AFP blood test. The Expanded AFP blood test is widely available and can be performed at a woman’s obstetrician’s office. Blood for this test can be drawn at 15 - 20 weeks of pregnancy. Information booklets with details on the Expanded AFP test are available at your doctor’s office.
It is important to note that these tests are only screening tests, not diagnostic. Most women with a positive screening test result are carrying a healthy baby. Women with a positive test result are subsequently offered diagnostic testing.
Read our Integrated Screen Welcome Sheet.
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Ultrasound
An ultrasound examination uses high frequency sound waves to create a visual image of fetal structures. Extensive studies to date show no evidence of ill effects or harm to the fetus by these sound waves. Other studies have shown that it is possible to detect many birth defects early in pregnancy that would otherwise go undetected until birth. The ultrasound also allows evaluation of the number of fetuses present, fetal growth, due date confirmation, determination of placental position, and other information about the pregnancy that can be useful to you and your doctor.
Fetal Echocardiogram
In pregnancies that are at increased risk for congenital heart disease, we can perform a detailed evaluation of the fetal heart structure, called a fetal echocardiogram. In most cases, a fetal echocardiogram can detect serious life-threatening congenital heart abnormalities.
Targeted Ultrasound Examination
In pregnancies at increased risk for specific genetic conditions or physical abnormalities, ultrasound may be used to examine a specific organ system or part of the body in an attempt to detect these problems before birth. This is called a targeted ultrasound examination.
All of our ultrasound equipment is leading-edge and of the highest caliber (GE Voluson(TM) and Siemens Sequoia(TM). We have the capacity to perform 3-D evaluations of fetuses at all of our offices. Three-dimensional ultrasound can be useful to better delineate certain birth defects and to help patients visualize the findings.
A thorough ultrasound examination is performed on all patients at the Prenatal Diagnosis Center before they undergo any genetic diagnostic procedure. The ultrasound is also used to guide the CVS or amniocentesis procedures. Our Ultrasound Department is accredited by the American Institute in Ultrasound Medicine (AIUM).
As with virtually all medical tests, ultrasound is not perfect. Because of factors that can develop later in pregnancy or interfere with the ability to clearly see all of the internal fetal structures, not all birth defects will be detected with this technology.
Carrier Screening
Individuals may have an increased chance of being a carrier of some genetic diseases based on their ethnic background. For example, cystic fibrosis (CF) is more common in Caucasians and thalassemia is more common in Asian patients. Other individuals may be at risk for an inherited disorder because it is present in their family. Our genetic counselors will discuss what carrier screening options may be appropriate for you. These tests usually involve a simple blood test.
Read more about cystic fibrosis screening (pdf file)
Read more about Ashkenazi Jewish disease screening (pdf file)
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