Pregnancy
PRENATAL GENETIC TESTING
By Emily Bloch
Expectant parents almost always have one thing in common: They're hungry for information about the health of their baby. Here, a chart on tests that can detect the presence of birth defects and other abnormalities:
| Test | What is it? | What can it detect? | Are there any risks? | Who gets it? | When? |
| Maternal serum screening | A simple blood
test that screens for levels of alpha- fetoprotein (AFP), as well as the hormones estriol and hcG |
Indications of
the risk of your baby having a brain, spinal, or abdominal -wall defect, or Down syndrome |
No,
though there is a chance of a "false positive" --a result that says your risk is high, when it really isn't. This chance would be ruled out by one of the diagnostic tests described below |
All pregnant women | 15 to 18 weeks;
results are usually available within 1 to 2 weeks after your
appoin- tment |
| Ultra- sound |
A
procedure in which a practitioner moves an instrument --often resembling a wand --across your abdomen or places a small device inside your vagina, in order to produce an image of your fetus on a video monitor |
The age and gender of your fetus, how fast it's growing, the location of your placenta, if you're carrying twins, and whether your fetus has a neural-tube defect | No, though there is a chance of a false positive, as with maternal serum screening | Women
who have abnormal blood- screening results, whose doctors want to
confirm the age of the fetus, or who have any potential problem. Some
doctors offer ultra- sound to all pregnant women |
Depends
on the reason for the ultra- sound; if it's in response to an abnormal screening result, usually very soon after those results are in |
| Amnio- centesis |
This
is a very accurate diagnostic test, in which a doctor, guided by an
ultra- sound, inserts a needle in your abdomen and draws a small sample of amniotic fluid |
Evidence of neural-tube defects, Down syndrome, and other chromo-somal defects; it can also determine the gender of the fetus | Yes. Side effects include cramping, vaginal bleeding, and leaking of amniotic fluid. While the chance of something happening to your fetus is rare, 1 in 200 women has a miscarriage due to this procedure | Women who have a family history of birth defects, who already have a child with a birth defect, or who are age 35 or older. It is also done to double-check the screening tests, such as AFP | 14 to 18 weeks; it can take 3 weeks for the results |
| Chorionic villus sampling (CVS) | Chorionic villi are the tissue that make up the placenta; since the villi come from the same fertilized egg as the fetus, they share the same genetic makeup and contain a lot of information about your fetus' health. To obtain cells, your doctor withdraws a small amount of tissue from placenta by inserting a catheter into your vagina or a needle through your abdomen | centesis |
Yes. The most common risk is miscarriage. One in 100 women has a miscarriage she would not normally have had because of CVS | Women
with similar situations as those who get amnio- centesis; the difference is that CVS can be performed up to a month before amnio, so you can be sure of the status of your pregnancy earlier on |
10 to 12 weeks; results are available within 3 weeks |
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The content on these pages is provided as general information only and should not be substituted for the advice of your physician.
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