No-Risk Tests for Down Syndrome

 
While amniocentesis and CVS are available to the small population at risk of giving birth to a child with chromosomal abnormalities, what about the over 90% of mothers who would like a no-risk test to see if their unborn child is healthy? The following section will outline various non-invasive techniques available to the mother to determine the health of the baby.

Blood Tests

Fetal Cells in the mother's Circulation

- During pregnancy, cells from the baby and the placenta travel throughout the mother's circulation. Thus, a blood sample from the mother can contain fetal cells that can be analyzed for chromosomal abnormalities. The only limitation of this technique is the inability to concentrate the fetal cells for analysis. Sometimes, an abnormal result may need to be confirmed with CVS or amniocentesis.

Serum Screening Tests

- Down Syndrome

· Studies have shown that a combination of maternal blood tests during weeks 15-18 is a cheap alternative to test for Down syndrome. The test looks for low levels of alpha fetoprotein (AFP) and high levels of human chorionic gonadotrophin (HCG) which have been shown to be the best method of screening for Down syndrome.

- Neural Tube Defects

· Maternal serum AFP tests are used at 15-18 weeks to determine whether the fetus has a neural tube defect. Since AFP exists in high concentrations in the cerebrospinal fluid surrounding the spinal cord and brain, increased AFP levels in the mother signify an unclosed neural tube in the fetus.

Cervical Washings

- A small amount of fluid can be injected into the cervical area with a syringe drawing up the placental cells collected in the fluid. This is known as cervical washing and if a pure sample is obtained, cells can be cultured and analyzed for chromosomal abnormalities.

Ultrasound

- At 18-20 weeks

· Some studies have shown that through observing signs such as fluid at the back of the neck, length of long bones, bowel appearance and amount of fluid in the kidneys, physicians can diagnose Down syndrome at an 80% accuracy rate. In reality, the actual percent may be lower and generally a clinic that detects 1/3 of Down syndrome fetuses at 18-20 weeks is doing well.

- At 10-13 weeks

· Particularly at 10-13 weeks, ultrasound scans have shown that Down syndrome fetuses have a fluid layer of 3 mm or more at the back of the neck, known as nuchal edema. It is critical to note that this sign is temporary; the fluid layer resolves itself by week 18. It ultimately appears that the best preventative measure involves an ultrasound at 10-13 weeks and an early serum screening test.

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