Prenatal Diagnosis Center
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:
Full 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 is performed at 10-14 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 is performed at 15-20 weeks of pregnancy and consists of an additional blood test and a detailed ultrasound at 18-20 weeks.
The Full Integrated Screen is an option available at the Prenatal Diagnosis Center.
It is important to note that this is only a screening test, 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 more about Full Integrated Screen and other Prenatal Screening from the California Department of Public Health's California Prenatal Screenng Program.
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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.
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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.
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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™ and Siemens Sequoia™). 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.
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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 Genetic Tests & Screens from Genzyme Genetics.
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