What to Expect From Prenatal Genetic Testing

However, remember that it is a screening test and still requires a confirmatory chorionic villous sampling (CVS) or amniocentesis to make the definite diagnosis. A screening test does not diagnose a condition. It should not be used to make decisions for treatment or pregnancy termination, but rather should be used to determine whether the mother wishes to have diagnostic prenatal testing performed.

The primary benefit of this screening test is that it can be performed earlier in the pregnancy and is much less invasive than a CVS or amniocentesis.

Next steps after receiving abnormal screening results

If a screening test indicates a higher-than-average risk, your health care professional may want to perform a basic ultrasound, which can help determine the gestational age of the fetus and show if a woman is carrying twins. If either of these factors accounts for the abnormal screen test result, no further testing is needed. Otherwise, a more detailed ultrasound examination may be performed, which allows a look at the baby's brain and spinal cord, as well as other parts of the body. This ultrasound can often identify an open neural tube defect or other malformation associated with an abnormal screening test.

Your health care provider may suggest you consider either amniocentesis or CVS. Both are diagnostic tests to determine whether the fetus actually has the disorder in question. Amniocentesis is performed more frequently and should be the choice if you're at risk for having a child with neural tube defects (CVS doesn't detect neural tube defects).

If you have amniocentesis, a doctor will use a needle to withdraw a sample of amniotic fluid (the fluid surrounding the fetus) for analysis. The procedure is typically performed during the second trimester, at 15 to 18 weeks.

Amniocentesis or CVS is offered for high-risk pregnancies, which could include any of the following: