Pregnancy can be an exciting time for expectant parents. It can also be a time of concern over the health of the baby. Medical technology has led to the development of many prenatal screening tools used to identify mothers and babies who are at an increased risk for developing a disease or condition.
Prenatal screening results do not give a “yes” or “no” answer about the presence of a disease or whether it will develop, only if it is more or less likely. Women who test positive for a screening test may not actually have the condition. The screening is a way to rule out people who are at low risk and identify those at high risk.
Birth defects are physical abnormalities that may be caused by inherited genes, genetic mutations, or environmental factors. They cause deformities or disabilities that cannot always be treated or cured. Birth defects that are most often identified by screenings are chromosome abnormalities like
and neural tube defects like spina bifida.
Screenings to Monitor Health of the Fetus
Screenings also enable doctors to monitor the health of a fetus during development. In many cases, when screenings produce abnormal results, subsequent testing will be recommended. Usually a combination of two or more of these screenings will produce the most reliable results. Some screenings are routine, while others are prompted by certain criteria, such as a mother’s age or abnormal results of a routine screening.
Examples of screenings include:
An ultrasound uses sound waves to produce a picture of the baby on a computer screen. It can determine the age of a fetus. The test can also identify twins, evaluate fetal structure, study breathing, and measure amount of amniotic fluid. An ultrasound may be done at anytime during the pregnancy. In the first trimester it can be done to make sure the age of the fetus is known. In the second trimester it is often done to evaluate fetal structure.
Nuchal Translucency (NT)
This screening assesses a baby’s risk for Down syndrome in the first trimester. It uses ultrasound to measure the space in the tissue at the back of the fetus’ neck, where fluid tends to accumulate if Down syndrome is present. The results of this test can indicate the need for further testing.
Triple Screen and Quad Screen
The triple screen looks for three specific substances in the mothers blood:
- Alpha-fetoprotein, which is a protein produced by the fetus
- hCG (human chorionic gonadotropin), which is a hormone produced within the placenta
- Estriol, which is an estrogen produced by the fetus and the placenta
Abnormal levels of the substances can indicate possible Down syndrome or other chromosomal abnormalities. It can also help identify neural tube defects.
In addition to these three substances, the quad screen also looks for Inhibin-A, which is a protein produced by the placenta and ovaries. This test may be better able to identify Down syndrome. The false positive rate of the test is low.
Cell-Free Fetal DNA Testing
This is a blood test that can detect the amount of the fetal DNA in the mothers blood. This test can help identify babies at increased risk for certain chormosomal abnormalities early in the pregnancy.
Non-stress Test (NST)/Biophysical Profile (BPP)
These tests are sometimes done with high-risk pregnancies to monitor the baby’s heartbeat and observe fetal activity, muscle tone, and breathing, as well as amniotic fluid volume.
Psychological Aspects of Screening
Screenings can be stressful for the parents, especially when results are abnormal and difficult decisions have to be made based on the screening information. While the screenings may help prepare parents for unexpected outcomes of the pregnancy, there may be no treatment that can be given while the fetus is still in utero.
Nonetheless, some who test positive for a screening will test negative in follow-up diagnostic tests.
Genetic counseling, an important component of prenatal screenings, can assist parents in understanding what the results mean, evaluating treatment options, and considering the possible need for further testing.