BLOGS

NIPT (Non-Invasive Prenatal Testing) or Combined testing for Screening Down Syndrome ?

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The main difference is accuracy: NIPT (Non-Invasive Prenatal Testing) analyzes fetal DNA directly from maternal blood, making it much more accurate and providing earlier results with fewer false positives than the Combined Test, which uses maternal age, blood markers, and an ultrasound (NT scan) to calculate risk. The Combined Test estimates risk (e.g., 1 in 100 chance), while NIPT gives a higher or lower chance with better precision, identifying most affected babies with very low false positives. 

Combined Test (First Trimester Screening)

1. Method: Combines maternal blood tests (hormones/proteins) and an ultrasound measurement (nuchal translucency, or NT) with maternal age.
2. What it does: Calculates a risk score (e.g., 1 in 500) for Down syndrome, Edwards syndrome, and Patau syndrome.
3. Accuracy: Less accurate; can have higher false positives, especially with age.
4. Timing: Usually done around 11-14 weeks. 

NIPT (Non-Invasive Prenatal Testing)

1. Method: A blood test analyzing cell-free fetal DNA from the placenta in the mother's blood.
2. What it does: Directly detects extra fragments of DNA for specific chromosomes (21, 18, 13).
3. Accuracy: Highly accurate, identifies nearly all affected babies with very low false positives (fewer than combined test).
4. Timing: Can be done earlier, from around 10 weeks. 

Key Takeaways

1. NIPT is more accurate and specific, detecting more actual cases and giving fewer false alarms.
2. Combined Test is a risk calculation, while NIPT looks at DNA.
3. You can often choose NIPT as a follow-up to a high-risk Combined Test or even instead of it.
4. Both are screening tests, not diagnostic; high-risk results usually lead to diagnostic tests like amniocentesis.