Is non-invasive blood drawing?

Non-invasive testing is basically a maternal examination that most pregnant women will undergo, and non-invasive testing mainly tests DNA. Non-invasive tests can effectively detect the growth of the fetus in the pregnant woman's body and whether the pregnant woman has any diseases that may affect the fetus. For example, pregnant women of advanced pregnancy who are undergoing in vitro fertilization need to undergo non-invasive tests. But in the process of non-invasive testing, is blood drawn for examination?

Does non-invasive DNA require a second blood draw?

According to the "Technical Specifications for Prenatal Screening and Diagnosis by High-throughput Gene Sequencing (Trial)" (hereinafter referred to as the "Specifications") issued by the National Health and Family Planning Commission, non-invasive DNA is a method of prenatal screening and diagnosis using gene sequencing technology. It only requires collecting more than 5 ml of peripheral venous blood from pregnant women and extracting fetal free DNA fragments contained in maternal peripheral plasma. Through the new generation of high-throughput DNA sequencing and bioinformatics analysis, the genetic information of the fetus can be obtained and the risk of the fetus suffering from chromosomal aneuploidy can be detected.

According to the guidelines issued by the National Health and Family Planning Commission, the accuracy rate of non-invasive DNA is over 90%, among which the detection rates of the three common chromosomal diseases, trisomy 21, trisomy 18 and trisomy 13, are no less than 99%, 97% and 90% respectively. The composite false positive rate should be less than or equal to 0.5%; the composite positive predictive value should be greater than or equal to 50%.

In view of the limitations of current medical testing technology and various reasons such as individual differences among pregnant women, the regulation also gives suggestions: the results of non-invasive DNA prenatal testing showing low risk are not the final diagnosis, and there is still the possibility of missed detection. Even for pregnant women whose screening results show high risk, the pregnancy should not be terminated hastily, and subsequent invasive prenatal diagnosis can be performed. Interventional prenatal diagnosis includes amniocentesis, cord blood puncture, chorionic villus sampling, etc., which are mainly used to prevent the birth of children with Down syndrome.

When to do non-invasive DNA

Non-invasive DNA is one of the prenatal check-up items. Non-invasive DNA refers to non-invasive DNA prenatal testing, non-invasive fetal chromosome aneuploidy testing, etc. The most widely used technology internationally is called NIPT, which is defined by a committee of the American College of Obstetricians and Gynecologists.

According to the guidelines of the National Health and Family Planning Commission, the best time for non-invasive DNA testing is from 12 weeks of pregnancy to (22 weeks + 6 days). If the pregnancy time exceeds the upper limit (gestational age > 22 weeks + 6 days), the detection risk increases; if it is too short (gestational age < 12 weeks), it will also affect the accuracy of the screening results. Therefore, most pregnant women choose to do non-invasive DNA prenatal testing at 14-18 weeks of pregnancy.

There are three main types of pregnant women suitable for non-invasive DNA prenatal testing:

1. In the prenatal screening report, the risk rate test value of Down syndrome is 1/1000≤1/270, the risk rate test value of 1/1000≤18-trisomy syndrome is 1/350, and the risk rate test value of 1/1000≤13-trisomy syndrome is 1/350, which means that serological screening and imaging examinations show that common chromosomal aneuploidy is close to high risk.

2. Contraindications to invasive prenatal diagnosis such as threatened abortion, fever, bleeding tendency, and unresolved infection during pregnancy.

3. The baby is in a later gestational age (20 weeks + 6 days or more) and happens to be within the time when non-invasive DNA prenatal testing can be performed. The baby has missed the best time for serological screening or prenatal diagnosis, but has special requirements for reducing the risk of three major chromosomal diseases.