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Prenatal Testing: Trust But Verify?

Prenatal testingPrenatal testing and screening have become more common in the United States in recent years. One of the reasons is that testing and screening procedures are increasingly offered to women who are not determined to be at risk of having a baby with a genetic defect or chromosomal disorder such as Down syndrome. Another reason is that easier, less invasive and more accurate tests have become available. As a result, testing and screening of pregnant women seem far more common than previously.

When they are deciding whether to be screened or tested, women should know the difference between testing and screening. It's pretty simple: Screening assesses the risk of having a baby with a particular condition, while testing is a diagnostic tool to determine whether a baby actually has the condition.

Conditions That Can Be Diagnosed Or Screened With Prenatal Testing

Testing and screening can be performed to identify numerous conditions or the risk of having a child with a condition. These conditions include:

· Down syndrome

· Tay-Sachs disease

· Spina bifida

· Cystic fibrosis

· Sickle cell disease

· Hemophilia

· Thalassemia

· Abdominal wall defects

· Kidney defects

· Esophageal defects

· Heart defects

These are just some of the conditions that can be diagnosed or screened for prenatally. In all, there are around 800 defects and illnesses that can be identified or ruled out through testing and screening.

Why Should Parent(s) Have Prenatal Tests?

Women have these tests for two primary reasons. One is to identify defects that can be corrected before birth. For example, some heart problems can be repaired in utero, reducing the risk that a baby will be born with the defect undetected and suffer significant damage as a result. The other major reason for having prenatal testing is that it will give parents information that can affect their decision-making. For example, some parents who are informed that their baby has a significant birth defect might choose to terminate the pregnancy or evaluate their financial resources differently in light of the information.

Types And Risks Of Prenatal Testing

A variety of techniques and procedures can detect the presence or likelihood of birth defects. Some are quite risky, while others are no more dangerous than a routine blood draw. Some are extremely accurate, while others simply suggest the probability of having a child with a particular condition. The most common tools are:

Ultrasound: This technique uses sound waves to create an image of the fetus. It allows practitioners to determine if a baby is growing normally. It also allows doctors to measure the accumulation of fluid at the back of the neck; excess fluid could be a sign of Down syndrome or significant heart defects. Ultrasound is generally thought to carry little or no risk to the baby, although numerous Internet articles have linked sonograms, as ultrasounds were once called, to childhood conditions such as autism. The validity of these articles is unknown.

Blood tests: Routine blood draws can determine whether the mother has certain conditions such as diabetes or lacks immunity to diseases such as rubella (also known as German measles) that are known to cause birth defects. Blood tests are also used to detect fetal proteins that are found in the mother's blood that can indicate spina bifida, Down syndrome and trisomy 18 (also known as Edwards syndrome). Blood tests are performed at different stages of the pregnancy depending on factors such as maternal age, medical history and the results of earlier screenings and tests. Blood tests can produce hematomas and arterial punctures in mothers; neither of these is usually very serious.

Amniocentesis: Amniocentesis involves inserting a needle into the uterus to remove amniotic fluid that is then tested for genetic defects. It can also be used to check for fetal or maternal infection or to evaluate the severity of an Rh incompatibility between mother and baby. The most common complication is miscarriage, which occurs in one in 300 women who are tested. Much less common injuries include needle injuries to the baby, leaking amniotic fluid and Rh sensitization.

Chorionic villus sampling (CVS): This test involves removing a small amount of placental tissue that is used to test the DNA, chromosomes and enzymes of the fetus. The test is conducted by inserting a thin catheter or needle either through the abdomen or through the cervix. In both instances, the technician is guided by ultrasound. It does not confirm the presence of all defects, but it can be performed earlier in a pregnancy than amniocentesis. It is also used to determine paternity. The primary risk is miscarriage, which occurs in one of 100 procedures.

One of the greatest dangers in having prenatal testing and screening performed is not the procedures themselves, but the reliability of the results reported from the tests and screenings. Incorrect reports might fail to identify fetal defects or incorrectly report problems. While the accuracy of these tests is generally good, medical practitioners should always schedule follow-up testing if there is any doubt or surprise about the results of a test or screening procedure. Failing to follow up appropriately could be seen as malpractice in some cases.


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