Your Baby Today

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	somal problems to amnio- 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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About The Author

Emily Bloch is a regular contributor to Your Baby Today.

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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.