What do I need to bring for Down syndrome screening?

Down syndrome screening is a common problem at present, which has a great impact on people's body. If people don't pay attention to it in daily life, it will cause a lot of trouble. What exactly is needed for Down syndrome screening will make many people very worried and at a loss. They are very worried that they may suffer a lot of pain in the process. Regarding Down syndrome screening, let me introduce it to you below.

What do you need to prepare for Down syndrome screening?

Down screening is the abbreviation for prenatal screening test for Down syndrome. The purpose is to determine the risk of the fetus suffering from Down syndrome by testing the pregnant woman's blood. What we now call Down syndrome screening is more accurately called prenatal screening. There are three main target diseases for screening: trisomy 21 (Down syndrome), trisomy 18 (Edwards syndrome), and open neural tube defects.

Trisomy 21 (Down syndrome) has an incidence of 1/700-1/800, trisomy 18 (Edwards syndrome) has an incidence of 1/6000-1/8000, and open neural tube defects have an incidence of 1/1000-1/2000.

First, the doctor will provide detailed genetic counseling for the expectant mother, such as the dangers of screening target diseases such as Down syndrome, the significance and limitations of serological screening. The expectant mother will then decide whether to choose screening and will need to sign an informed consent form.

Then, the doctor will confirm some basic information with the expectant mother on the day of blood collection (including date of birth, last menstrual period, weight, whether she has insulin-dependent diabetes, twins, whether she smokes, history of abnormal pregnancy, etc.). If necessary, the expectant mother will be asked to undergo B-ultrasound to ensure the accuracy of the gestational age. Since the calculation of the risk value for screening requires certain corrections based on the above information, it is very important to fill in this information before blood is drawn.

Down syndrome screening can detect 60-70% of children with Down syndrome. It should be made clear that the Down syndrome screening test can only help determine the chance that the fetus has Down syndrome, but it cannot determine whether the fetus has Down syndrome. That is to say, when the blood test index is high, the chance of having a Down syndrome baby is higher, but it does not mean that there must be something wrong with the fetus.

Young pregnant women under the age of 34 should undergo Down syndrome screening, which can be performed between 15 and 20 weeks of pregnancy, and preferably between 16 and 18 weeks. Pregnant women who are over 34 years old, women with Down syndrome in their family, and women who have given birth to children with Down syndrome are already at high risk, so they do not need to undergo Down syndrome screening. Instead, they should go directly to non-invasive DNA or amniocentesis or chorionic villus sampling.

Currently, the Down syndrome screening test tests the concentration of alpha-fetoprotein (AFP) and human chorionic gonadotropin (β-hCG) in the pregnant woman's blood, and combines it with the pregnant woman's age to use a computer to accurately calculate the risk of each pregnant woman carrying a fetus with Down syndrome.

The normal value of alpha-fetoprotein should be 0.4~2.5MoM. The lower the test value, the higher the chance that the fetus will suffer from Down syndrome. The higher the level of chorionic gonadotropin, the higher the chance that the fetus will have Down syndrome. In addition, the doctor will input the alpha-fetoprotein value, human chorionic gonadotropin value, as well as the pregnant woman's age, weight, and weeks of pregnancy into the computer, which will calculate the risk of the fetus developing Down syndrome.

If the test results show that the risk is lower than 1/270, it means that the risk is relatively low and the chance of the fetus having Down syndrome is less than 1%. However, if the risk is higher than 1/270, it means that the fetus is at high risk of disease and further amniocentesis or chorionic villus sampling should be performed.