Britcher Leone Blog

A primer on prenatal screening

On Behalf of | May 24, 2022 | Birth Defects |

A pregnant woman and her health care team use several methods of prenatal screening tests to get a better idea of the health of the developing fetus and to provide information about potential genetic abnormalities. These screening tests provide valuable information to help assess the pregnancy and to guide conversations about additional testing, if indicated. Sometimes, medical intervention can be offered. Prenatal screening allows physicians to use family history, biochemical assays and ultrasound measurements to identify potential risks of birth defects, disorders or conditions including:

  • Down’s syndrome. This is a genetic disorder that can result in intellectual disabilities. It is present in about 1 out of every 700 infants.
  • Trisomy 18. Also known as Edward’s Syndrome, Trisomy 18 is a genetic disorder that occurs when there are three, instead of two, copies of chromosome 18. Trisomy 18 is severe. Medical professionals note that 95% of pregnancies with Trisomy 18 end in miscarriage or stillbirth.
  • Spina bifida. This is a neural tube defect. Spina bifida happens when the neural tube does not fully close anywhere along the spine. This can lead to damage to the spinal cord and nerves and can contribute to physical and intellectual disabilities.

What are the prenatal screening tests?

There are various testing options depending on the stage of the pregnancy. One option available early on is cell-free DNA. This is a blood test used at 10 weeks of pregnancy. It can determine the fetus’ sex as well as provide information to help determine the risk of chromosomal disorders like Down’s syndrome and Trisomy 18.

Nuchal translucency, human chorionic gonadotropin (hCG), and PAPP-A are a series of tests performed during the 11-13 weeks of pregnancy. Medical professionals use these tests, also referred to as the first-trimester screen, to review the pregnant woman’s blood tests, as well as an ultrasound of the fetus to look for heart disorders and chromosomal abnormalities. Another option, chorionic villus sampling (CVS), involves the woman’s medical team collecting a sample of tissue from the pregnant woman’s placenta. This test occurs during 10-13 weeks of pregnancy and looks for inherited disorders like cystic fibrosis, as well as chromosomal abnormalities.

The second trimester quad screen test and an amniocentesis are available during the second trimester of pregnancy. The second-trimester quad screen test is an integration of four different tests: the AFP, hCG, estriol, and inhibin-A. These tests measure the levels of hormones and proteins within the pregnant woman and fetus and can indicate the risk of chromosomal abnormalities, as well as spinal and abdominal defects within the fetus. This screening test is generally available from 16 to 18 weeks of pregnancy. The amniocentesis is available from 15 to 20 weeks of pregnancy and tests the amniotic fluid. This fluid contains cells shed from the fetus, as well as enzymes, proteins, and hormones. Testing this fluid can provide valuable information about the risk for genetic disorders and neural tube defects. Examples can include Down syndrome, cystic fibrosis, Tay Sachs disease, and spina bifida, as well as potential infection.

Ultrasound around the 20th week of pregnancy allows for a fetal anatomical survey, which looks closely at vital organs, such as the brain, heart, kidneys and other organs to identify additional defects that may be life-threatening or even incompatible with life. Cardiac structure, brain development and spine development can be evaluated at this time. While not all abnormalities are discernible, many are and this information is important for expecting parents and physicians.

Medical professionals recommend these testing options so the pregnant woman and her medical team make important decisions about care for both her and her developing fetus. These tests, as with any medical test, come with risks, so it is important for the expectant mother and her doctor to engage in shared decision-making about the best medical care plan.