You might know that some prenatal tests screen for Down syndrome and other chromosomal disorders, but you may not have heard of microdeletions. This type of chromosomal disorder is more common than you might think, but not all microdeletions cause health problems.
Here's what parents need to know about microdeletions, including how they're detected.
What is a microdeletion?
A microdeletion is an abnormality that occurs when a piece of a chromosome is missing. In fact, it’s just what it sounds like: micro (tiny); deletion (taken away).
You might remember from high school biology that virtually all of our cells contain chromosomes with DNA; we get 23 from each parent for a total of 46.
Throughout your life, your cells replicate by dividing — and in the process, your body chops up these DNA strands to make them more manageable to use. But once in a while, a tiny bit of a chromosome is removed during this process, resulting in a microdeletion.
The effect a microdeletion has on your baby’s health and development depends on its location and size. Some microdeletions can cause intellectual disability, problems with motor skills or miscarriage, while others do no damage at all.
How common are microdeletions?
Unlike other chromosomal abnormalities, which are more likely to occur in moms with certain risk factors (such as those who are 35 years or older or who have a family history of a genetic disorder), microdeletions seem to occur randomly (which means they don’t usually run in families) and equally affect any baby regardless of other risk factors.
In fact, by some estimates nearly all of us have some microdeletion in our chromosomes. For example, 22q11.2 deletion syndrome is rare and occurs in about one out of 4,000 people. But this condition may be underdiagnosed, which means it could occur more frequently.
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Will a NIPT include microdeletions?
One test that is widely ordered after 9 weeks for moms-to-be is the non-invasive prenatal test (NIPT). This is a blood test that provides information about the health of your still-developing baby.
NIPT screens for the most common chromosomal disorders: Trisomy 21 (Down syndrome), Trisomy 18 (Edwards syndrome) and Trisomy 13 (Patau syndrome). An expanded NIPT screens for five chromosome pairs and may detect specific microdeletions.
But NIPT is just one in a series of tests a doctor can do to inform you about your developing baby and possible health outcomes.
Although NIPT has a 99 percent overall detection rate of chromosomal abnormalities, it is still a screening test and is not definitive. If your family has a history of intellectual developmental disorder, you may want to consider going beyond NIPT and having your practitioner order other tests such as amniocentesis or chorionic villus sampling (CVS) with the addition of microarray testing.
Microarray testing can only be performed on an amniocentesis or CVS. These tests are more advanced than NIPT and are capable of looking at chromosomes to find out if any of them are missing a small part of DNA or if they have extra information.
What does it mean if I get a positive result?
If an expanded NIPT detects a microdeletion, remember that this is not a diagnostic test, and can’t tell you with 100 percent accuracy that your baby has a particular condition — they only give you a calculation of the odds. If it’s high enough, your doctor may recommend consulting with a genetic fetal medicine specialist or having additional testing, such as CVS, amniocentesis or a microarray test — invasive tests with a very small risk to your baby but that diagnose with certainty.
If further testing determines your baby has a microdeletion, knowing in advance can help you take steps to improve her health and quality of life. While there is no cure, a variety of therapies are available. As soon as your baby is born, you can work with medical specialists for a thorough evaluation to treat cardiac, neurological, palate, bone, immune, hearing or vision problems.
For example, babies with 22q deletion syndrome have a harder time maintaining calcium in their bodies — so prenatal testing ensures doctors know they need to monitor these levels from birth and supplement as necessary.
Knowing your baby has a microdeletion might seem scary, but many parents find learning about the condition prior to birth empowering, as it allows them time to prepare and assure the best and safest outcomes.
Other parents may feel anxious and worried before getting tests like NIPT, CVS and amniocentesis. If this is the case for you, consider talking to a genetics counselor about what positive test results could mean for your baby.
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