NIPT or the double screening test?

NIPT (Non-Invasive Prenatal Test) or the Double Test for Down Syndrome screening?

The main difference is sensitivity:
NIPT (Non-Invasive Prenatal Test) analyses fetal DNA taken directly from the mother's blood, so it provides much higher accuracy, gives results earlier than the Double Test, and has a much lower false-positive rate. The Double Test calculates risk using maternal age, blood tests and ultrasound findings (NT measurement). NIPT, on the other hand, reports a high or low probability more precisely and detects most affected babies with a very low false-positive rate.

Double Test (First Trimester Screening Test)

1. Method: Performed by combining hormone/protein values in the mother's blood with the nuchal translucency (NT) measurement and maternal age.
2. What it does: Calculates a risk ratio (for example 1/500) for Down syndrome, Edwards syndrome and Patau syndrome.
3. Accuracy: Lower accuracy; the false-positive rate may increase, especially at an advanced age.
4. Timing: Usually performed between the 11th and 14th weeks of pregnancy.

NIPT (Non-Invasive Prenatal Test)

1. Method: Performed by analysing cell-free fetal DNA originating from the placenta in the mother's blood.
2. What it does: Directly detects excess DNA fragments, particularly those belonging to chromosomes 21, 18 and 13.
3. Accuracy: Very high accuracy; it catches almost all affected babies and the false-positive rate is quite low.
4. Timing: Can be performed earlier; from about the 10th week.

Key Points

1. NIPT is more accurate and more specific; it detects true cases better and gives fewer false results.
2. The Double Test is a risk calculation, whereas NIPT looks at DNA.
3. NIPT may be preferred after a high-risk Double Test result or directly instead of it.
4. Both are screening tests, not diagnostic tests; in the case of high-risk results, diagnostic tests such as amniocentesis are mostly recommended for a definitive diagnosis.