Diagnostic Testing Information
At Carilion Clinic's Prenatal Diagnostic Center we perform the following diagnostic tests and procedures:
Alpha-fetoprotein Analysis
During normal development, the fetus produces a substance called alpha-fetoprotein (AFP), some of which passes through the placenta into the mother’s bloodstream. By drawing a blood sample, it is possible to identify women more likely to be carrying a fetus with certain physical abnormalities.
An elevated level of AFP may indicate a malformation of the baby’s spine or brain, called a neural tube defect. However, a high AFP value may simply mean that the baby’s gestational age was miscalculated, or that the mother is carrying twins. If no explanation for the high value can be found, genetic counseling and further evaluation is recommended.
Amniocentesis
This procedure is usually performed around the 17th week of pregnancy. It involves removing a sample of fluid from the sac in which the fetus is developing. Cells in this fluid contain genetic material that can be tested for specific genetic defects. Amniocentesis is routinely used to detect chromosomal abnormalities and neural tube defects.
Chorionic Villous Sampling
Also known as CVS, this diagnostic procedure is performed between 10 and 12 weeks gestation. In this procedure, a small amount of tissue is removed from the fetal side of the placenta using either a vaginal or abdominal approach. The cells from this tissue are analyzed for specific genetic disorders.
Fetal Echocardiography
A fetal echocardiogram is a specialized type of ultrasound to view the baby’s heart. This test makes it possible to identify abnormalities in the heart structure and irregularities in heart rate. The procedure is often used when there is concern about the presence of a heart defect in the baby.
Percutaneous Umbilical Blood Sampling
Another method of obtaining a sample from the fetus is percutaneous umbilical blood sampling (PUBS). Guided by high-resolution ultrasound, the doctor inserts a needle through the mother’s abdomen into the umbilical cord and withdraws a sample. This test is usually reserved for high-risk situations.
Quad Screen Analysis
The analysis of four markers, in combination with a woman’s age, is believed to detect 75 percent of women at increased risk for having an infant with Down syndrome. The four markers evaluated in this test are alpha-fetoprotein (AFP), unconjugated estriol (uE3), human chorionic gonadotropin (hCG) and dimeric inhibin A (DIA).
If a quad screen analysis suggests an increased risk for Down syndrome, additional diagnostic testing is offered. An abnormal quad screen does not mean the baby has Down syndrome – it simply means the chance is increased. The quad screen may also test positive if the gestational dates are incorrect.
Sonogram/Ultrasound
This test uses high-frequency sound waves to obtain detailed pictures of the developing fetus. Sonography has been available for over 20 years and is safe for both the baby and mother. A number of structural birth defects can be detected with this method.
