NIPT (Non Invasive Prenatal Test)
NIPT is performed on a maternal blood sample which contains DNA from the fetus.
During pregnancy, there are cell-free DNA fragments (cfDNA) from both the mother and fetus in maternal circulation. It is possible to analyze cell-free DNA to detect fetal trisomies such as Down syndrome (trisomy 21).
- Fetal anomalies on ultrasound
- Known genetic anomalies that cannot be diagnosed by NIPT
NIPT was developed and is performed by the ARIOSA laboratory in the USA under the Clinical Laboratory Improvement Amendments (CLIA).
The sensitivity of NIPT to exclude Down syndrome (trisomy 21) is very high: if NIPT is normal, the residual risk for trisomy 21, trisomy 18 and trisomy 13 is < 1 on 1.000. The specificity of NIPT for the chromosomes tested is > 99%, which means that in less than 1 on 100 pregnancies an abnormal NIPT result is obtained although the fetus has normal chromosomes.
- In case of a normal NIPT result: no specific follow up is necessary unless ultrasound examination of the fetus reveals anomalies and further fetal studies might be indicated.
- In case of test failure: in a limited number of pregnancies (< 4%) not enough fetal DNA can be extracted from the maternal blood, and NIPT cannot be performed. This has no implications on the risk of fetal aneuploidies or other fetal anomalies. In these pregnancies NIPT can be repeated at no extra cost on a repeat maternal blood sample.
- In case of an abnormal NIPT result: in case of an abnormal result, the physician or genetic counseler will discuss the implications of such chromosomal anomaly with the patient, who can then decide to confirm the NIPT results with chromosome studies after amniocentesis or chorion biopsy.