Non-invasive Gene Detection: Which Fetal Abnormalities Can Be Screened?

The 30-year-old Liu was told by the hospital that the test results of Down’s screening she did at the 16th week of pregnancy showed [high risk], that is, the risk of her fetus suffering from Down’s syndrome (also known as [fetal trisomy 21] or Down’s syndrome) was higher. Doctors advised Ms. Chen to further confirm the diagnosis by amniocentesis.

However, amniocentesis is traumatic after all, and the risk of abortion is relatively high. If you don’t do it, you worry that if you really have bad luck and give birth to a Down’s son, the consequences will be unimaginable. Do it or not?

Just when Ms. Liu’s family was at a loss, they overheard friends say that there is now a way to test whether the fetus is healthy by taking a drop of blood from the mother, so they came to the clinic for consultation.

Q: Is there a way to know whether the fetus is good or bad by pumping the mother’s blood? Is it really that divine?

A: In recent years, there has been a new prenatal detection technology called [non-invasive gene prenatal detection technology (also called non-invasive DNA prenatal detection)] to detect fetal chromosome abnormalities. However, it is not as divine as you said. It is impossible to know whether the fetus is healthy with [a drop of blood].

DNA is the carrier of human genetic information. Pregnant women have a very small amount of fetal free DNA in their blood. Using a new generation of DNA sequencing technology to sequence these fetal free DNA fragments and analyze biological information, fetal genetic information can be obtained from them.

Because it is only necessary to draw venous blood from pregnant women, we call it a [non-invasive] detection method compared with invasive [amniocentesis].

It should be emphasized that non-invasive gene prenatal testing is only aimed at the detection of some chromosome number abnormalities and cannot replace amniocentesis or B-ultrasound examination. In short, all necessary tests during pregnancy are very important and cannot be replaced by each other. It is impossible to know all the problems of the fetus through a certain test.

Q: What items can this non-invasive gene prenatal test do at present?

A: Non-invasive gene testing can be used to detect whether the fetus has abnormal chromosome number. Human beings have 23 pairs of chromosomes. If one more or one less chromosome is found, it will cause physical abnormalities. This is abnormal chromosome number.

However, because this method requires data accumulation, At present, three kinds of chromosome diseases are applied to clinical detection: trisomy 21, trisomy 18, trisomy 13, etc., that is, one more chromosome 21, chromosome 18 or chromosome 13. Trisomy 21 syndrome is familiar to everyone and is also the most common. Trisomy 18 syndrome and trisomy 13 syndrome are also accompanied by intellectual development disorders, somatic deformities and other problems.

Q: Is the accuracy of non-invasive gene prenatal testing high?

A: At present, the accuracy rate of non-invasive gene detection for the above three chromosome diseases can reach 99%.

Q: Since the accuracy rate is so high and there is no trauma, why can’t non-invasive gene prenatal testing replace amniocentesis?

A: Although non-invasive gene prenatal testing has such high accuracy, However, it cannot be used as the final diagnostic standard. Only amniocentesis can make the final diagnosis. There are 23 pairs of human chromosomes, Amniocentesis can detect all 23 pairs of chromosomes in a more comprehensive way. It can not only check chromosome number abnormalities, but also find some large chromosome structure abnormalities, while non-invasive gene prenatal detection only does three pairs of chromosome number abnormalities at present. Therefore, non-invasive gene prenatal detection cannot replace amniocentesis, and amniocentesis karyotype analysis is still the gold standard method for fetal chromosome examination.

Children with Down’s syndrome

Q: I found out that it is only trisomy 21 with high risk. Can we know whether the fetus is really Down’s syndrome by doing non-invasive gene prenatal testing?

A: If only trisomy 21 syndrome is excluded, it is possible to do non-invasive prenatal genetic testing. But again, the accuracy rate is not 100%, so so far we still define this technology as prenatal screening with high accuracy rate, but it is not a definite diagnosis. If you want to know other chromosomes, you need amniocentesis.

Q: What if non-invasive gene prenatal testing is also a high risk?

A: If non-invasive gene prenatal testing is also a high risk, then further final diagnosis through amniocentesis is needed.

Q: Is it more appropriate to do this examination at what time?

A: Detection can be carried out over 12 weeks of gestation, and the best detection time is 12-23 weeks of gestation; If you exceed this gestational week and really need to do it, you need to consult a doctor.

Q: Is it necessary to have an empty stomach for non-invasive gene prenatal testing?

A: No, the routine diet will not affect the test results.

After the consultation, Ms Liu considered it for a moment. Finally decided to do non-invasive gene prenatal testing, Although the types of examination are less than amniocentesis, but at least there is no damage to the mother’s body. Three weeks later, the test results are low risk, which shows that 99% of the confidence can exclude the fetus from 21-trisomy syndrome, 18-trisomy syndrome and 13-trisomy syndrome. Ms. Liu finally breathed a sigh of relief. Through the follow-up obstetric examination, the baby is also all normal.

A new non-invasive prenatal detection technology for genes, As a more accurate screening method for Down’s syndrome, This has brought more choices to expectant mothers in need. The suitable population includes: pregnant women with critical risk of Down’s screening for trisomy 21-or trisomy 18-syndrome, pregnant women with contraindications for invasive prenatal diagnosis (such as active infection, central placenta previa, threatened abortion, etc.), pregnant women who have missed serological screening time, etc.

However, the types of chromosome abnormalities diagnosed by this technology are still limited and all chromosome abnormalities cannot be found. In short, due to the limitations of non-invasive gene prenatal testing, careful consideration is needed and careful consultation is required. Doctors will need to formulate individualized prenatal screening and prenatal diagnosis programs according to the specific conditions of pregnant women.

Responsible Editor: Xiaoyan

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