Prenatal diagnosis consists of the detection of fetal conditions before birth. Detection of such diseases has been mainly performed by non-invasive techniques using a combination of ultrasound and maternal serum screening or via invasive techniques such as amniocentesis or cordocentesis. Invasive tests consist of fetal DNA collection through the insertion of a needle and may carry risks such as fetus loss and fetal abnormalities.
Discovery of cfDNA
The presence of fetal cell-free DNA (cfDNA) in the maternal bloodstream was discovered 19 years ago and has changed the way prenatal diagnosis is performed. At first, it was used mainly to qualitatively detect the presence of characters present only in the fetus and not in the mother like sex determination (detection of chromosome Y) and the RHD fetal genotype (detection of Rh+ bearing fetuses in Rh- mothers).
Next Generation Sequencing
With the advance of next generation sequencing, it became possible to detect quantitative traits. This has mainly been applied for aneuploidies (chromosome loss or gain), especially Down syndrome (Trisomy 21). It is performed through the detection of an increase or decrease of fetal DNA present in maternal blood. For instance, if there is 10% of fetal material and the fetus is affected by Down syndrome, a 5% increase of chromosome 21 will be detected in the blood.
The First Non-Invasive Prenatal Test
In 2011, the first non-invasive prenatal test (NIPT) was made commercially available for the detection of the most common trisomies (Trisomy 21, 18 and 13). Since then, several tests have been launched, including detection of other aneuploidies and smaller gain/loss of genetic material. Although NIPT has a high sensitivity and specificity (especially for trisomies), it is yet considered a screening test, and in the case of positive result, confirmatory invasive tests must be performed.
The Future of Prenatal Diagnosis
With the advance and development of genetic testing, the focus will be on improving non-invasive prenatal diagnosis techniques. The question remains, however, how should and how will such information be used.
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