Demystifying Down syndrome screening during pregnancy: Here’s everything you need to know

Pregnancy is a special moment for every family. In some cases, the fetus may suffer from some genetic diseases, and Down syndrome is one of them. In order to identify fetuses with Down syndrome in advance, Down syndrome screening during pregnancy has become an important prenatal examination project. This article will reveal the secrets of Down syndrome screening during pregnancy and let you know more about Down syndrome screening.

What is Down syndrome ?

Down syndrome screening for pregnant women is a test method used to screen for Down syndrome in the fetus. Down syndrome is a common chromosomal abnormality, also known as trisomy 21 in medicine, because normal human chromosomes are two, but because there are three chromosomes in chromosome 21, it is trisomy 21. The extra chromosome may cause mental retardation, congenital heart disease, hydrocephalus, etc. in the child. Among them, mental retardation is the most important manifestation of this syndrome. The face of the child also has certain typical characteristics, such as wide eyes, poor development of the bridge of the nose and nasal bones, and easy tongue extension. In addition, some children may have combined through palms, that is, the middle fingers of both hands are connected to the palm, which is commonly known as "broken hands". Down syndrome is a congenital disease related to genetic factors, so every pregnant woman is required to do Down syndrome screening in the early or middle pregnancy to avoid the birth of defective children.

What does Down syndrome screening during pregnancy check?

It is the abbreviation of prenatal screening test for Down syndrome, which is one of the necessary items in prenatal check-up. Currently, the commonly used Down syndrome screening programs include early pregnancy combined screening (9 weeks to 13 weeks and 6 days of pregnancy), mid-pregnancy serological screening (15 weeks to 20 weeks and 6 days of pregnancy), and early and mid-pregnancy combined/sequential screening. This screening method combines the age of the pregnant woman, blood tests and ultrasound examinations to assess the risk of Down syndrome.

In the Down syndrome screening during pregnancy, the following aspects are mainly checked:

Fetal nuchal translucency thickness (NT value): Through ultrasound examination, the thickness of the fetal nuchal translucency is measured. People with Down syndrome usually show a thicker nuchal translucency in this examination.

Blood biochemical markers of pregnant women: A small portion of the pregnant woman’s blood is drawn for testing to detect specific markers in the blood, such as free β-hCG and human chorionic gonadotropin-A (PAPP-A).

What should I do if the risk of Down syndrome screening is high?

Down syndrome screening during pregnancy is not absolutely accurate. It only gives the possibility of having Down syndrome based on a series of information and statistical data. The screening results are usually expressed as the risk ratio (such as 1/1000) or percentage (such as 0.1%) of the disease. It should be noted that the screening results may have false positives (pregnant women with normal results are mistakenly diagnosed as high risk) and false negatives (pregnant women with Down syndrome are mistakenly diagnosed as low risk). Therefore, after obtaining the screening results, the doctor will further discuss with the pregnant woman and develop a subsequent diagnostic plan.

Non-invasive fetal DNA testing (NIPT): This is a non-invasive test performed using a blood sample that allows for a more detailed analysis of the fetal genome to assess the risk of chromosomal abnormalities such as Down syndrome. The test has a high detection rate and a low false positive and false negative rate.

Amniocentesis or chorionic villus sampling: This is an invasive test that extracts a sample of amniotic fluid from the uterus for chromosome analysis. The test results are relatively accurate, but because it is invasive, there are certain risks, such as infection or miscarriage, and it is expensive. Therefore, doctors usually only recommend amniocentesis in high-risk situations.

Things to note when doing Down syndrome screening during pregnancy :

Time: For pregnant women between 14 and 21 weeks of pregnancy, the best time is between 15 and 18 weeks;

Age: There is no age limit for pregnant women, but pregnant women over 35 years old are usually considered to be in the high-risk group;

Screening process: Before undergoing Down syndrome screening, you should consult a doctor to understand the purpose, process and possible results of the screening, and choose the appropriate screening method according to the doctor's advice. On the day of screening, pregnant women need to collect venous blood samples on an empty stomach to measure the concentrations of serum alpha-fetoprotein (αFP), unconjugated estriol (uE3) and free β-human chorionic gonadotropin (F-βHCG); during the screening, you should relax and avoid excessive tension; if the test results show abnormalities, you should seek medical treatment in time to prevent delays in the disease and affect the normal growth and development of the fetus.

In short, Down syndrome screening during pregnancy is a non-invasive detection method. Pregnant women with a high-risk value above the critical value do not necessarily have a fetus with Down syndrome. Therefore, expectant mothers should not worry too much, stay in a good mood, and do not add too much psychological burden to themselves. They should maintain a positive attitude, follow the doctor's advice, and have regular pregnancy checkups to ensure the health of themselves and the fetus. (Du Xinli, Lingshou County People's Hospital, Shijiazhuang City, Hebei Province)