NIPT is a screening test that examines the DNA of the baby in the mother's blood. It can determine the possibility of Trisomy 21 (Down syndrome), Trisomy 18, and Trisomy 13, with results indicating positive, negative, or pending status.
As maternal age increases, the likelihood of giving birth to a baby with Trisomy 21 (Down syndrome) or Trisomy 18 also increases.
A small amount of blood is collected from the mother between 10 and 16 weeks of pregnancy, and fragments of DNA in the blood (cfDNA: cell-free DNA) are analyzed.
Approximately 10% of the cfDNA in the mother's blood comes from the placenta and is essentially the same DNA as the fetus. By analyzing this, the possibility of Trisomy 21 (Down syndrome), Trisomy 18, and Trisomy 13 in the fetus can be determined. However, the severity of the condition or the symptoms cannot be determined.
Additionally, it takes about two weeks to receive the results. If the test results are "positive" and the patient may wish to undergo amniocentesis for a definitive diag-nosis, it is recommended to undergo the test by around 15 weeks of pregnancy at the latest.
The results for the fetus will indicate either 'positive,' 'negative,' or 'pending' for Tri-somy 21 (Down syndrome), Trisomy 18, and Trisomy 13.
NIPT is known for its high accuracy for Trisomy 21 (Down syndrome), but the accu-racy for Trisomy 18 and Trisomy 13 is not as high as for Trisomy 21. However, since this is a non-diagnostic test, if the result is positive or pending, amniocentesis is recommended for a definitive diagnosis.
According to the NIPT Consortium (*), the positive predictive value and negative predictive value for each of Trisomy 21 (Down syndrome), Trisomy 18, and Trisomy 13 are as follows:
For example, if the result is positive for Trisomy 21 (Down syndrome) in a 40-year-old mother, the positive predictive value is approximately 94% (the probability that the baby actually has the condition). However, if the result is positive for Trisomy 18, the positive predictive value is about 50%.
On the other hand, the negative predictive value is over 99% for all conditions, mak-ing it a highly reliable test.
If the result is pending, genetic counseling will be provided, and the couple will need to decide whether to retake the NIPT, undergo amniocentesis for a definitive diag-nosis, or not pursue further testing.
＊An organization that many accredited NIPT facilities belong to.
Sensitivity: 99.1%, Specificity: 99.9%
| Age | Disease Frequency※ | Positive Predictive Value | Negative Predictive Value |
|---|---|---|---|
| 30 | 1/626(0.16％) | 61.3％ | 99.99％ |
| 35 | 1/249(0.40％) | 80.0％ | 99.99％ |
| 40 | 1/68(1.47％) | 93.7％ | 99.98％ |
| 45 | 1/16(6.25％) | 98.5％ | 99.94％ |
※The probability of a mother at 12 weeks of pregnancy carrying a baby with Trisomy 21, using the values from Snijder (1999)
Sensitivity: 99.9%, Specificity: 99.6%
| Age | Disease Frequency ※ | Positive Predictive Value | Negative Predictive Value |
|---|---|---|---|
| 30 | 1/2100(0.15％) | 10.6％ | 99.99％ |
| 35 | 1/840(0.12％) | 22.9％ | 99.99％ |
| 40 | 1/230(0.43％) | 52.2％ | 99.99％ |
※The probability of a mother at 16 weeks of pregnancy carrying a baby with Tri-somy 18, using the values from Snijder (1999).
Sensitivity: 91.7%, Specificity: 99.7%
| Age | Disease Frequency※ | Positive Predictive Value | Negative Predictive Value |
|---|---|---|---|
| 30 | 1/6500(0.015％) | 4.5％ | 99.99％ |
| 35 | 1/2600(0.038％) | 10.5％ | 99.99％ |
| 40 | 1/700(0.14％) | 30.4％ | 99.99％ |
※The probability of a mother at 16 weeks of pregnancy carrying a baby with Tri-somy 13, using the values from Snijder (1999).
Changes in Positive and Negative Predictive Value Based on Incidence Rates Quoted from the NIPT Consortium Patient Information Materials.
| NIPT (Non-Invasive Prenatal Testing / Non-Invasive Prenatal Genetic Screening) | ￥99,000(including tax ￥108,900) |
|---|
※The fees are subject to change without prior notice.
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・Since the test only requires a maternal blood sample, the risk of miscarriage is min-imal.
・High negative predictive value.
・High positive predictive value for Trisomy 21 (Down syndrome).
・Since NIPT is a non-diagnostic test, amniocentesis is required for a definitive diag-nosis if the NIPT result is positive.
・If the result is inconclusive, the next steps can be difficult to decide.
