Non-invasive prenatal testing (NIPT) has been developed for nearly 20 years. In the early days of its promotion, it was highly sought after by mothers-to-be inland, many of whom traveled over the mountains and through the stars to Hong Kong for this test because it could find out the sex of the fetus. The technology is non-invasive and accurate, and many high-risk mothers-to-be underwent the test because they did not want to undergo the puncture test.
What diseases can be detected by NIPT, does a clean NIPT result mean that the baby must be fine, and can NIPT replace ultrasound prenatal screening? The ultrasound team at the Department of Obstetrics and Gynecology at the First Hospital of Sun Yat-sen University today will explain briefly and unveil the mystery of NIPT.
Mother’s blood contains fetal DNA fragments, an amazing discovery!
The discovery of large fragments of fetal free DNA in maternal plasma in 1997 was a remarkable discovery. It broke the previous situation where the examination of fetal chromosomes relied solely on puncture tests. So, NIPT is a good option to analyze fetal DNA by drawing the mother’s blood.
What diseases can NIPT detect?
The ability of NIPT to check fetal DNA non-invasively by drawing the mother’s blood to rule out chromosomal disorders is a great advancement. However, NIPT is not a panacea. With the current technology, NIPT is mainly used to detect trisomy 21, 18, 13, sex chromosomes and aneuploidy. 99.0% of trisomy 21, 96.8% of trisomy 18 and 92.1% of trisomy 13 are detected, which is a very high rate. However, the detection of microdeletion and microduplication syndromes by NIPT is yet to be further confirmed, and genetic lesions are undetectable.
So we can see that NIPT is able to detect only a few diseases, which are very limited. And fetal abnormalities include millions of structural and functional abnormalities, and only a small percentage of these abnormalities are combined with chromosomal problems, and a small percentage of the small percentage are the problems that can be detected by NIPT. Therefore, a clean NIPT result does not mean that the fetus is completely clean! It only means that the fetus has a very low probability of having 21, 18, 13-trisomy and other aneuploidy disorders. These are the most common chromosomal disorders in fetuses, and the ability of NIPT to accurately and non-invasively detect these disorders is a milestone in the development of fetal medicine.
The significance of prenatal ultrasound screening
Prenatal ultrasound screening can detect structural abnormalities in the fetus, including and not limited to 21, 18, 13-trisomy and other aneuploidy problems. Any fetal abnormality, including various chromosomal disorders, with severe structural abnormalities in the fetus has the opportunity to be detected by ultrasound and the patient is directed to undergo a puncture test to confirm the diagnosis.
With the common application of high-resolution color Doppler ultrasonography, after years of joint efforts and accumulation of domestic and foreign obstetric ultrasonographers, experienced ultrasonographers can now achieve more than 90% detection rate for trisomy 21 in middle pregnancy; trisomy 18 and trisomy 13 will lead to multiple serious fetal abnormalities, and prenatal ultrasound is more likely to detect these abnormalities and is less likely to miss the diagnosis; for microdeletion syndromes such as 22 For microdeletion syndrome such as chromosome 22 microdeletion, which causes special structural abnormalities in the fetus, prenatal ultrasound can also detect them; for genetic lesions, such as bone development-related genetic lesions and kidney development-related genetic lesions, although ultrasound cannot determine the type of genetic lesions, as long as the fetus has abnormalities in related organ structures, ultrasound can detect and suggest the possibility of related diseases and guide patients to further examination to confirm the diagnosis.
This is why prenatal ultrasound screening is an irreplaceable test!
How to analyze the results of NIPT
NIPT is also a screening test and not a diagnostic test. Therefore, the results only show risk values, but unlike the risk values provided by traditional combined screening, NIPT only reports a low risk (1:10,000) or a high risk (99%) for each chromosome, which are the only two results that are more intuitive and not entangled.
Do you need a NIPT?
The current recommendation is to divide the mothers-to-be into very high risk (≥1:10), intermediate risk (1:11-1:2500) and low risk (<1:2500) groups according to the combined screening. This can detect 98% of trisomy 21, 18 and 13.
NIPT tips (the latest recommendations from international fetal medicine experts)
1.The average time for NIPT results is about 10 days (21-28 days for invasive puncture tests, and the same day for ultrasound), and the results are available within 14 days in more than 95% of cases, with less than 2% of cases failing to produce results in 3-4 weeks, when a new blood draw may be required.
2, the cost of NIPT is about 500-2500 euros, almost 1700-3000 yuan in China, and most of them are self-funded, which is much higher than the existing feasible screening technology.
3, Chimerism may not be detected.
4. Maternal blood contains at least 3-4% free DAN fragments of fetal origin. The percentage of free fetal DNA in maternal blood is so low at less than 10 weeks of gestation that reliable results are not available.
5. It is common for overweight or obese pregnant women to be unable to obtain test results.
6. Problems in the collection or delivery of the sample may affect the results of the test.
7. The efficacy of the test in twin pregnancies is still being further confirmed.
NIPT advantages.
1, NIPT is a non-invasive test, currently applied to detect fetal trisomy 21, 18, 13-, sex chromosomes and aneuploidy, with a high detection rate for the most common chromosomal disorders.
2.The accuracy of NIPT is higher than that of combined screening, and it can correct the risk value of the latter, but the fee is higher, so families with financial conditions can try it.
3, NIPT can detect only a limited number of chromosomal disorders and cannot replace prenatal ultrasound screening, but you can still trust the ultrasonographer’s discerning eye.