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 may not give a “yes” or “no” answer about the presence of a disease or whether it will develop, but if it is more or less likely. Women or fetuses with a positive screening test may not actually have or develop the condition (false positive) or may develop the condition even if the screen is negative (false negative). The screening may only identify those at high risk.
Birth Defects
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 Down syndrome and neural tube defects like spina bifida.
Screenings to Monitor Health of the Mother
A woman’s health directly impacts the health of her fetus. At the first prenatal care appointment, the healthcare provider will review the mother’s family and personal health history and offer routine screenings so issues that could threaten the fetus can be controlled or anticipated.
Routine screenings may include:
- Blood pressure measurement
- Urine tests to detect urinary tract infection, protein in the urine, and signs of gestational diabetes
- Lab analysis for infections, such as gonorrhea, chlamydia, and group B streptococcal disease
- Blood tests for:
- Blood type and Rh factor
- Other sexually transmitted diseases, including HIV infection
- Hepatitis
- Antibodies for rubella
- Anemia
- Diabetes
Some screening tests may be done under specific circumstances. These may include:
- Hereditary diseases like cystic fibrosis, sickle cell disease, Tay-Sachs disease, and thalassemia
- Thyroid function testing
Screenings to Monitor Health of the Fetus
Screenings also enable healthcare providers 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 2 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:
Ultrasound
An ultrasound uses sound waves to produce a picture of the baby on a computer screen. It can be used to determine fetal age. The test can also identify twins (or more), 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 or Turner 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 or Turner syndrome is present. The results of this test can indicate the need for further testing.
NT can also be used during this time to screen for congenital heart defects in fetuses without chromosome abnormalities. Further testing can be done later in the pregnancy with a fetal echocardiogram.
Triple Screen and Quad Screen
The triple screen looks for 3 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 (spina bifida).
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.
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 like Down syndrome or Trisomy 18 early in the pregnancy.
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 like Down syndrome or Trisomy 18 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 with fetal activity, fetal movement and tone, and breathing, as well as amniotic fluid volume. Non-stress tests are done late in the pregnancy if there is a high risk of complications or stillbirth.
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.
It is important to recognize that 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.
RESOURCES
American Pregnancy Association http://americanpregnancy.org
Office on Women's Health http://www.womenshealth.gov
CANADIAN RESOURCES
The Society of Obstetricians and Gynaecologists of Canada http://sogc.org
Women's Health Matters http://www.womenshealthmatters.ca
References
FAQ: Cell-free fetal DNA testing. UCSF Medical Center website. Available at: https://www.ucsfhealth.org/education/cell-free%5Fdna%5Fscreening/index.html. Accessed June 14, 2016.
First trimester screen. American Pregnancy Association website. Available at: http://www.americanpregnancy.org/prenataltesting/firstscreen.html. Updated July 2015. Accessed June 14, 2016.
Prenatal tests. March of Dimes website. Available at: http://www.marchofdimes.org/pregnancy/prenatal-tests.aspx. Updated March 2015. Accessed June 14, 2016.
Prenatal ultrasound screening. EBSCO DynaMed website. Available at: http://www.ebscohost.com/dynamed. Updated February 5, 2016. Accessed June 14, 2016.
Routine prenatal care. EBSCO DynaMed website. Available at: http://www.ebscohost.com/dynamed. Updated April 24, 2016. Accessed June 14, 2016.
Screening tests for birth defects. The American Congress of Obstetricians and Gynecologists website. Available at: http://www.acog.org/Patients/FAQs/Screening-Tests-for-Birth-Defects. Updated April 2014. Accessed June 14, 2016.
Special tests for monitoring fetal health. The American Congress of Obstetricians and Gynecologists website. Available at: http://www.acog.org/Patients/FAQs/Special-Tests-for-Monitoring-Fetal-Health. Updated November 2013. Accessed June 14, 2016.
STDs during pregnancy. Centers for Disease Control and Prevention website. Available at: http://www.cdc.gov/std/pregnancy/STDFact-Pregnancy.htm. Updated May 20, 2016. Accessed June 14, 2016.