A More Accurate Test

DNA is the building block of chromosomes. Humans have 23 pairs of chromosomes in each of their cells. Half of these chromosomes are received from the father and half are received from the mother. Any mutations involving an abnormal number of chromosomes will cause serious health problems, such as early-stage miscarriage, abnormal organ development, and irreversible mental or developmental retardation. The most significant example is Down syndrome, caused by trisomy (i.e. triple copies) on chromosome 21.

Research conducted around the world has confirmed that NGS technology can determine the sequence of both fetal and maternal DNA using a sample of the mother's blood. The ratio of each type of chromosome is then calculated using bioinformatics software. NGS technology is far more accurate than blood serum screening when detecting mutations involving an abnormal number of chromosomes. Indeed, blood serum screening can only reveal the probability that the fetus has a genetic disease.

You may be wondering why the detectability factor of NIPS isn't 100% if this test does not calculate probabilities. The answer is that the concentration of fetal DNA in maternal blood varies at different stages of pregnancy and with the physical condition of the mother. Generally speaking, NIPS is less accurate result when the concentration of fetal DNA is lower than 2.5%. Moreover, test results can be inconclusive or erroneous if the mother herself suffers from chromosome abnormalities, has undergone a transplantation procedure, or has a history of cancer.

Multiple studies have confirmed that the concentration of fetal DNA in maternal blood is negatively correlated with the BMI of the mother. In other words, the blood of heavier women has a lower concentration of fetal DNA, which in-turn reduces the accuracy of the test.

Although NIPS can be used to examine the 23rd chromosome, the law forbids physicians from using this test to reveal the gender of the baby.