How to Detect Chromosomal Abnormalities

Chromosomal abnormalities, which can cause conditions like Down syndrome and Turner syndrome, may worry you as a parent-to-be or new parent. However, keep in mind that they're fairly rare and often manageable. It's also good to know that there are several tests that can be done during pregnancy and after birth to detect chromosomal abnormalities with a high degree of accuracy. Read on for answers to some of the key questions you might have about identifying chromosomal abnormalities.

Question 1 of 8:

When should I do screenings during pregnancy?

Do fetal ultrasounds and blood tests in the first and second trimesters. In the U.S., the testing regimen is typically broken down by pregnancy trimester. While your testing plan should be individualized based on your circumstances, it’s safe to expect something like the following:^{[1]XTrustworthy SourceCenters for Disease Control and PreventionMain public health institute for the US, run by the Dept. of Health and Human ServicesGo to source}
- First trimester: initial ultrasound of the fetus and blood testing of the mother.
- Second trimester: a more detailed ultrasound of the fetus, possibly a fetal echocardiogram, and more detailed maternal blood screening to look for signs of specific chromosomal abnormalities in the fetus.
- As needed (second/third trimester): high-resolution ultrasound, amniocentesis (testing of fluid surrounding the fetus), chorionic villus sampling (CVS—testing a piece of the placenta).
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Question 2 of 8:

Can a fetal ultrasound detect an abnormality?

In many cases, yes, but additional testing is always needed for diagnosis. It's always most likely that an ultrasound will accurately detect no sign of chromosomal abnormalities. That said, the first trimester ultrasound may miss out on signs of abnormalities that are more likely to be picked up during the second trimester ultrasound, ideally done at around 18 weeks. If a potential chromosomal anomaly is found, additional testing such as amniocentesis and chorionic villus sampling (CVS) is necessary.^{[2]XTrustworthy SourcePubMed CentralJournal archive from the U.S. National Institutes of HealthGo to source}
- The standard two-dimensional (2D) ultrasound has long been used for screenings, but 3D and even 4D options are now available. The evidence is mixed, however, as to whether these more advanced ultrasounds are actually better at detecting chromosomal abnormalities.

Question 3 of 8:

How do fluid tests help diagnose a fetus?

Blood, placenta, and amniotic fluid tests identify markers of abnormalities. While ultrasounds look for physical signs of chromosomal abnormalities, fluid tests look for specific proteins and other markers that point to particular abnormalities. That’s why, even though chromosomal abnormalities are fairly rare, it’s important to use both ultrasounds and fluid testing to check for them.^{[3]XTrustworthy SourceCenters for Disease Control and PreventionMain public health institute for the US, run by the Dept. of Health and Human ServicesGo to source}
- A maternal blood screening (first trimester) checks for 2 proteins (hCG and PAPP-A) that can indicate fetal chromosomal abnormalities.
- A maternal serum screening (second trimester) checks the blood for 3 or 4 proteins that can indicate specific abnormalities like Down syndrome.
- During chorionic villus sampling (CVS), the doctor collects a small piece of the placenta and runs tests on it to check for markers of particular abnormalities.
- During amniocentesis (“amnio”), a small amount of the amniotic fluid that surrounds the fetus is collected and checked for cells that indicate chromosomal abnormalities.
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Question 4 of 8:

How are kids and adults diagnosed?

Look for common traits and use blood tests for confirmation. Chromosomal abnormalities aren’t always identified before birth, but certain physical, mental, behavioral, and/or medical traits can indicate abnormalities in kids and adults. Blood screenings that are similar to those done with fetuses are used to diagnose kids and adults. Watch for signs like the following:^{[4]XResearch source}
- Abnormally-shaped head
- Cleft lip (openings in the lip or mouth)
- Distinctive facial features, such as widely spaced eyes, small and low ears, drooping eyelids, flattened facial profile, short neck, or upward-angled eyes
- Low birth weight
- Little to no body hair
- Below average height
- Reduced muscle mass
- Defects of the heart, intestines, kidneys, lungs, and/or stomach
- Learning disabilities
- Infertility
- Other mental and physical impairments

Question 5 of 8:

What are the main risk factors?

The age of the mother, family history, and teratogens can play roles. Females are born with all the eggs they’ll ever produce, and the risk of chromosomal abnormalities increases once the eggs (and mother) are over 35 years old. A family history of chromosomal abnormalities is also a significant risk factor. Likewise, the mother’s exposure to teratogens, which are substances or conditions that contribute to birth defects in general, can increase the risk of chromosomal abnormalities.^{[5]XTrustworthy SourceUniversity of Rochester Medical CenterLeading academic medical center in the U.S. focused on clinical care and researchGo to source}
- Teratogens can include things like medications, illicit drugs, alcohol, tobacco, toxic chemicals, viruses and bacteria, radiation, and certain pre-existing health conditions.
- The older the birth mother, the more likely chromosomal abnormalities become. A 35-year-old mother has about a 1 in 192 chance of developing a fetus with a chromosomal abnormality. That rate increases to 1 in 66 by age 40.^{[6]XTrustworthy SourceMarch of DimesNonprofit organization devoted to improving the lives of mothers and babies.Go to source}
- Chromosomal abnormalities can be hereditary (passed down through generations) or spontaneous (occurring due to damage to the fetus’ specific genetic material).^{[7]XResearch source}
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Question 6 of 8:

Are there ways to reduce the risk?

Identify any risk factors and make healthy lifestyle choices. Chromosomal abnormalities are unlikely to begin with, but there's no way to completely eliminate the risk of a fetus developing one. That said, choices made by the genetic parents (especially the mother) can cut the risk of birth defects in general. The American CDC identifies several of these positive choices in what it calls the PACT plan:^{[8]XTrustworthy SourceCenters for Disease Control and PreventionMain public health institute for the US, run by the Dept. of Health and Human ServicesGo to source}
- Plan ahead: see your primary care doctor regularly before and during pregnancy, and take supplements like folic acid as advised.
- Avoid harmful substances: steer clear of potential teratogens like tobacco, alcohol, and illicit drugs, and don’t allow health conditions like infections and fevers go untreated.
- Choose a healthy lifestyle: stay physically active, aim to maintain a healthy body mass index (BMI), and treat chronic health conditions like diabetes.
- Talk with your healthcare provider: consult with them before taking medications or supplements or getting vaccinations.

Question 7 of 8:

Are chromosomal abnormalities common?

They affect around 1 in 150 to 1 in 250 babies born in the United States. It’s hard to get precise figures,^{[9]XTrustworthy SourceMarch of DimesNonprofit organization devoted to improving the lives of mothers and babies.Go to source} but it’s safe to say that chromosomal abnormalities are fairly uncommon but not extremely rare.^{[10]XResearch source} Chromosomal abnormalities also have a wide range of impacts—some go unnoticed while others have life-altering effects.
- Down syndrome is the most common chromosomal abnormality in the U.S. It occurs in about 1 in 365 babies born to 35-year-old mothers, and 1 in 100 babies born to 40-year-old mothers.^{[11]XResearch source}
- It can be scary to think about these statistics if you're a parent-to-be, but focus on the fact that they actually show that the odds are far greater that you'll have a child without any chromosomal abnormalities.
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Question 8 of 8:

Are there treatments available?

Chromosomal abnormalities can’t be cured, but can often be treated. Surgical procedures can sometimes repair physical impacts, such as heart defects, caused by chromosomal abnormalities. Overall, though, the goal for treating chromosomal abnormalities is to prevent future medical issues and promote a high quality of life. Treatments may include the following:^{[12]XResearch source}
- Genetic counseling to explain the condition, what to expect in the future, and how to strategize and cope with the situation.
- Occupational therapy to build quality-of-life skills like dressing, bathing, and eating.
- Physical therapy to improve motor skills and muscle development.
- Medications to control conditions commonly associated with chromosomal abnormalities, especially relating to the cardiovascular system.

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While the typical person has 23 pairs of chromosomes, chromosomal abnormalities occur when there is a problem with the number, structure, and/or characteristics of the chromosomes.^{[13]XResearch source}
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