Understanding NIPT and Microdeletions
Understanding NIPT and Microdeletions
What are Microdeletions?
Microdeletions are very small missing pieces of DNA on a chromosome. While large chromosomal differences like Down syndrome involve entire chromosomes, microdeletions affect much smaller regions. Depending on which genes are affected, they can sometimes cause learning difficulties, developmental delays, or other health issues — but this varies widely.
How Are Microdeletions Detected?
Some non-invasive prenatal tests (NIPT) include optional screening for a limited number of microdeletion syndromes. This is done by analysing fragments of placental DNA in the mother’s blood.
Although NIPT is very accurate for detecting common conditions like Down syndrome, it is much less accurate for rare conditions such as microdeletions.
What Microdeletions Can Be Screened?
|
Condition |
Region Affected |
Approximate Frequency |
Associated Features |
|
Chromosome 22 |
1 in 4,000 |
Heart defects, immune problems, learning difficulties |
|
|
Chromosome 1 |
1 in 5,000–10,000 |
Developmental delay, seizures |
|
|
Chromosome 5p15 |
1 in 20,000–50,000 |
Cat-like cry, intellectual disability |
|
|
Chromosome 4p16 |
1 in 50,000 |
Facial features, severe delays |
|
|
Chromosome 15q11–13 |
1 in 10,000–20,000 |
Feeding problems, behaviour differences |
Not all NIPT providers screen for every microdeletion listed here — and some only include them as optional add-ons.
Why Is Screening for Microdeletions Controversial?
• These conditions are extremely rare.
• The tests are prone to false positives.
• Positive Predictive Value (PPV) is low.
• This causes real distress for families.
Should I Screen for Microdeletions?
If you are considering NIPT, you may be offered the option to include microdeletion screening — but it’s worth pausing to consider the pros and cons carefully.
Ask yourself:
“If a test says my baby is at high risk of a rare condition, but there’s a very low chance it’s true – and the ultrasound scan looks completely normal – how will that make me feel?”
For many families, a ‘high risk’ microdeletion result leads to significant stress and anxiety, with invasive testing needed to confirm or exclude the diagnosis. In most cases, the baby turns out to be perfectly healthy.
Unless there is:
– a known family history of a specific microdeletion syndrome,
– or a structural abnormality seen on ultrasound,
…many women choose not to screen for microdeletions, especially given the low accuracy, low PPV, and high emotional burden.
What Happens If a Microdeletion is Suspected?
If your NIPT result suggests a possible microdeletion:
1. You will be referred for counselling with a specialist or genetic counsellor.
2. Further testing such as CVS or amniocentesis may be offered to check the baby’s chromosomes directly.
3. A detailed scan will be reviewed to look for structural abnormalities that may support or challenge the finding.
Summary: What You Should Know
|
Key Fact |
What It Means |
|
Microdeletions are rare |
Most pregnancies are unaffected |
|
NIPT is less reliable for microdeletions |
Results often need confirmation |
|
High false positive rate |
Many ‘high risk’ results are wrong |
|
Low PPV |
Even if your result is high risk, baby is very likely to be healthy |
|
Testing can cause anxiety |
Consider the emotional impact before deciding |
|
Scans are important |
A normal ultrasound reduces the chance of a true condition even further |
Final Advice
Before deciding to include microdeletions in your NIPT, it’s worth speaking to your healthcare provider. Think about:
– Your personal or family history
– Whether you’d want further tests if a result came back ‘high risk’
– How you might feel managing uncertainty during pregnancy
You are always in control — and making an informed choice is what matters most.
