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Prenatal Screening and Diagnostic Testing

Who Should Consider Prenatal Diagnostic Testing?

The American College of Obstetricians and Gynecologists (ACOG) recommends offering the option of chorionic villus sampling (CVS) or amniocentesis to all pregnant women for the prenatal diagnosis of chromosome abnormalities.

Testing should specifically be considered for women who:

  • Will be over the age of 35 at delivery
  • Have an abnormal screening test, such as a first trimester screen, quad screen, sequential screen, or noninvasive prenatal screening (NIPS)
  • Have certain abnormalities seen on ultrasound
  • Have had a previous pregnancy with a chromosome abnormality
  • Have an inherited predisposition to chromosome abnormalities
  • Are at risk for a prenatally diagnosable inherited genetic disorder

What is a CVS?

CVS is typically performed between 10 and one half weeks and 13 weeks of pregnancy. Depending upon the position of the placenta, CVS is performed either through the cervix with a catheter or through the abdomen with a needle. A small amount of the chorionic villi are removed from the developing placenta. These villi are finger-like projections that contain cells that are representative of the fetus. This sample is sent to the laboratory for chromosome analysis or any other special genetic testing. CVS procedures carry a small risk for miscarriage (up to 1%) and other complications.

What is an Amniocentesis?

Amniocentesis is typically performed between 15 weeks and 22 weeks of pregnancy. A thin needle is inserted into the woman’s abdomen and into the amniotic sac. A small amount of amniotic fluid is removed and sent to the laboratory for chromosome analysis or any other special genetic testing. Alpha-fetoprotein (AFP) is also found in the amniotic fluid and measured to assess the risk for open neural tube defects (birth defects that affect the brain, spine or spinal cord). Amniocentesis procedures carry a small risk for miscarriage (up to 0.5%) and other complications.

How Accurate are the Results from CVS and Amniocentesis?

Chromosome results from CVS and amniocentesis are greater than 99% accurate.

A wider array of testing on a CVS or amniotic fluid specimen may be suggested based on certain ultrasound findings when the potential cause is uncertain. More comprehensive testing, such as the Targeted Prenatal Array, can detect a wide variety of genetic disorders and may be considered in certain scenarios.

It is important to note that no method of prenatal testing (CVS or amniocentesis) can guarantee the birth of a healthy baby. CVS and amniocentesis are used to diagnose only the conditions for which the couple is known to be at risk (i.e., chromosome abnormalities or specific genetic disorders).