If you are a mother-to-be, I am sure you will hear many mothers-to-be ask during your maternity check-up: What is non-invasive DNA? Why did the doctor recommend me to have this test? Is there something wrong with the baby in my belly? ………… So, do you know what is non-invasive DNA? First of all, it is important to know that DNA is the material that transmits genetic information between parents and offspring, and each person has a specific DNA, which constitutes the difference between people. And, the said non-invasive DNA test, actually refers to non-invasive prenatal testing (non-invasive prenatal testing, NIPT) refers to the collection of peripheral blood from pregnant women for common aneuploidy screening using free nucleotides of fetal origin. first reported by Lo in 1997, and widely carried out with the development of second-generation sequencing technology. In China, it has been carried out rapidly in recent years due to birth defects and the widespread availability of prenatal screening. So what exactly are the conditions that require this so-called non-invasive DNA? Generally speaking, a mother-to-be, in early pregnancy around 12 weeks, will have an ultrasound examination (mainly to listen to the fetal heartbeat, exclude ectopic pregnancy and calculate the size of the fetus); at the same time fetal ultrasound NT (T fetal nuchal translucency) screening will be performed at the same time, and then a second Down’s screening will be performed around 5 churning 16 weeks. The main concern is the presence of chromosomal, or DNA, abnormalities, commonly trisomy 21, 18 and 13, which can lead to different mental and developmental disabilities after birth. If these screening results are questionable or indicate a high risk, then your doctor will recommend further testing. This includes non-invasive DNA and amniocentesis. Because of the risks associated with amniocentesis, noninvasive DNA is the most acceptable form of further testing. Non-invasive DNA testing, also known as non-invasive prenatal testing (NIPT), refers to the collection of peripheral blood from pregnant women and the use of free nucleotides of fetal origin for common aneuploidy screening. Internationally, there is the following guidance for the testing of non-invasive DNA December 2012 The American College of Obstetricians and Gynecologists (ACOG) in association with the Society for Maternal-Fetal Medicine (SMFM) issued the following guidance: 1. NIPT can be used as a primary screening method for those at high risk for chromosomal aneuploidy (older pregnant women over 35 years of age; ultrasound suggestive of abnormal soft indicators; previous history of childbirth with aneuploidy; one of the couples with a Roche translocation). 2, NIPT risk assessment is limited to 21, 18, 13-trisomy, which cannot completely replace prenatal diagnosis, and there is also a risk of test failure (due to insufficient fetal free DNA, etc.). 3. NIPT is not suitable for use in low-risk groups and twin births. In April 2013, the International Society for Prenatal Diagnosis (ISPD) stated that: 1. NIPT is less efficient in detecting trisomy 13; 2. Currently, clinically validated experiments focus on advanced age and screening of high-risk groups, and are not fully validated in low-risk groups; 3. In low-risk groups, the false-positive rate is similar to that of high-risk groups; 4. The accuracy of results will be affected by the presence of chromosomal chimerism; 5. Maternal fetal free DNA or other laboratory factors may cause test failure; 6. There is a lack of uniform standards for quality control and technical testing; 7. Pregnant women with high body mass index have an increased risk of test failure or inconclusive results; 8. Pregnant women in late pregnancy may lack sufficient time for repeat testing or prenatal diagnosis to make a definitive diagnosis, so NIPT should be recommended with caution in late pregnancy. June 2014 The International Society of Ultrasound in Obstetrics and Gynecology (ISUOG) recommends 1. direct interventional prenatal diagnosis is recommended in pregnant women of advanced age or with a history of chromosomal aneuploidy; 2. NIPT may cover only 70% of chromosomal abnormalities in pregnant women with serologic screening suggestive of very high risk (risk value >1:10), and interventional prenatal diagnosis is recommended even in the absence of ultrasound fetal structural abnormalities If the ultrasound is suggestive of fetal structural abnormalities, interventional prenatal diagnosis is recommended, regardless of whether the NIPT result is normal or not. As a mother-to-be who is recommended to undergo non-invasive DNA testing, you should know that: 1. The screening efficiency of non-invasive DNA technology for trisomy 21, 18 and 13 is higher than that of serological testing. 2. 2. There are many factors that affect the accuracy of the results, including: placental chimerism, maternal malignancy, maternal chimerism, one of the twin fetuses stopping, gestational week, and the amount of fetal free DNA in the maternal blood. 3.The best time for non-invasive testing is 12 weeks-26 weeks plus 6 days of pregnancy; the best time for amniocentesis is 14-20 weeks. 4.The advantages of non-invasive fetal DNA prenatal testing are: non-invasive, low risk; the disadvantage is that chromosomal ectopic cannot be seen, non-invasive provides indirect evidence, it is only a screening means, amniocentesis is the means to confirm the diagnosis. 5. For those who think there is a high risk, it is recommended to perform interventional prenatal diagnosis directly; because there is a certain false negative rate; and the chromosome examination items of amniocentesis are more than non-invasive examination.