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Prenatal Tests

''Is my baby healthy?" 

That's the question that moms-to-be worry the most about in pregnancy. You want assurances about your unborn child’s health.  That's where prenatal testing comes in. Many, but not all, conditions that can affect the baby’s health can be detected during pregnancy, often early enough to determine the special care your baby will need before and after birth.

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Here's a look at the most common prenatal tests you can expect to undergo at some point during your pregnancy. Some will be discussed in further detail later in this guide.

hCG: Human chorionic gonadotropin is a hormone that is produced by the placenta after a woman becomes pregnant. Its presence in blood or urine confirms pregnancy. Abnormally high amounts of the hormone are produced with multiple pregnancies (twins or triplets). It is also part of other prenatal tests done to detect birth defects. These tests are the quad marker screen and triple screen. High levels of hCG in a pregnant woman's blood may indicate that she is at risk for having a baby with Down syndrome and should therefore undergo amniocentesis for a more definitive diagnosis.

Alphafetoprotein (AFP or triple) screening: Most women can expect to get AFP testing during their pregnancy. It is a blood test that can indicate an increased risk for fetal neural tube defects, such as spina bifida (a deformity of the spinal column) or anencephaly (the absence of all or part of the brain). It can also indicate an increased risk of Down syndrome. AFP, hCG, and estriol are tested together and are referred to as a triple screen. The quad screen refers to a test that measures AFP, hCG, and estriol but adds inhibin to improve its accuracy. They both look for the same thing -- neural tube defects and Down syndrome. Low levels of AFP and estriol, particularly when combined with elevated levels of hCG and inhibin, may indicate a greater risk for having a baby with Down syndrome.

Ultrasound: Almost all women will have at least one ultrasound during their pregnancy. This test uses sound waves to make an image of your baby. During the ultrasound, the doctor can detect abnormalities in the baby. For example, they can see whether the baby's spine has developed normally. In addition, your baby's sex can sometimes be determined during an ultrasound.

Glucose screening: This is a test to determine if the mother is developing gestational diabetes (high blood sugar during pregnancy). This condition occurs in 3%-5% of pregnant women. Almost all women will have a glucose screen during pregnancy.

Amniocentesis: Recommended to pregnant women over age 35 or who are at high risk of giving birth to a baby with genetic or chromosomal disorders, this test removes a small sample of amniotic fluid for analysis.

Chorionic Villus Sampling: Like amniocentesis, CVS is a test used to detect birth defects in the baby. CVS can give results earlier in pregnancy than amniocentesis, allowing women the option to terminate their pregnancy earlier if something seriously wrong is detected. CVS can also be useful when amniocentesis is not possible (for example, when there is not enough amniotic fluid).

Cordocentesis: Also called fetal blood sampling or percutaneous umbilical cord sampling, this test collects fetal blood directly from the umbilical cord. This test can be used to look for low oxygen levels or anemia (low red blood cell counts) in the fetus. It is also performed to measure for maternal antibodies that may cause the mother's immune system to react unfavorably towards her fetus.

WebMD Medical Reference

Reviewed by Mikio A. Nihira, MD on August 15, 2012
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