Prenatal Testing

The Purpose of Prenatal Testing

Prenatal Testing is recommended for pregnant women who are at increased risk of having a child with genetic disorders such as Tay Sachs Disease, Cystic Fibrosis or Sickle Cell anemia, or developmental abnormalities such as Down’s Syndrome. This includes:

  • Women who have had abnormal results from a prenatal screening test.
  • Women who have had  a chromosomal abnormality or neural tube defect in a previous pregnancy.
  • Women age 35 or older.
  • Women with a family history of a specific genetic disorder, or she or her partner is a known carrier of a genetic disorder.
  • Women with a suspected uterine infection or Rh incompatibility.

Diagnostic Tests

Until very recently, the only way to diagnose  genetic disorders was to do an amniocentesis or chorionic villus sampling.  While chromosomal abnormalities were definitively diagnosed or ruled out, the slight increase in miscarriage due to the procedures was unacceptable.  So amniocentesis and chorionic villus sampling, while definitive test for chromosomal abnormalities, have been reserved for women at high risk of having a child with abnormalities or who have had positive results on screening tests.

Screening Tests

Prenatal screening tests have evolved rapidly in the past 20 years. Blood tests for Alpha-fetoprotein (AFP), the Triple Screen and the Quadruple Screen, all test for proteins put out by the developing fetus that can be measured in the mother’s blood.  But the AFP test has a high false positive rate and the Triple screen is only accurate in detecting Down’s syndrome about 60% of the time while the Quadruple screen is only accurate in predicting Down’s syndrome about 70 to 75% of the time. In 1995, The First Trimester Risk Assessment screen, a non-invasive prenatal screening test, became available in the United States.  All of the tests are summarized on this website.

Are Prenatal Screening Tests Mandatory?

While obstetricians will recommend prenatal screening tests to women who are at risk of having a child with genetic and/or developmental abnormalities, not all couples will have the test performed. Many couples are content to accept whatever the pregnancy brings and having prenatal screening will in no way impact how they are going to proceed.

Other couples prefer to have prenatal screen tests done so that they can plan how to proceed:

  • Undergo definitive diagnostic and genetic testing if needed
  • Prepare for a potentially complicated labor, delivery and post partum course
  • Prepare for a child that may have significant health and developmental needs
  • Terminate the pregnancy

There is no one way to screen for fetal abnormalities and no one way to manage abnormal results. The purpose of prenatal screening is to provide couples with information so that they can make wise health and life choices that suit their situations.