What are the components of prenatal screening for Down syndrome?
Apr 27, 2025
Source: Cainiu Health
Dr. Zhang Lu
Introduction
Under normal circumstances, prenatal screening programs for Down syndrome include serological screening for Down syndrome, ultrasound NT examination, non-invasive prenatal genetic testing, amniocentesis, and cordocentesis. It is advisable to undergo comprehensive preconception checkups before pregnancy, including chromosomal testing for both partners, to understand one's own physical condition. If there is a family history of genetic disorders or other high-risk factors, timely consultation with a physician and appropriate interventions should be considered.
Generally, prenatal screening programs for Down syndrome include serological screening for Down syndrome, ultrasound NT examination, non-invasive prenatal genetic testing, amniocentesis, and cordocentesis. A detailed analysis follows:
1. Serological Screening for Down Syndrome
Serological screening for Down syndrome is usually performed during the first and second trimesters of pregnancy. By drawing the pregnant woman's blood, the levels of certain biomarkers in the serum, such as alpha-fetoprotein (AFP), human chorionic gonadotropin (hCG), and unconjugated estriol (uE3), are measured. The levels of these biomarkers may be abnormal in pregnant women carrying a fetus with Down syndrome. Combined with factors such as maternal age and gestational age, the risk of the fetus having Down syndrome can be calculated.
2. Ultrasound NT Examination
Ultrasound NT examination is generally performed between 11 and 13 weeks of gestation. NT refers to the nuchal translucency, which is the thickness of fluid accumulation in the subcutaneous tissue at the back of the fetal neck. By measuring the NT value via ultrasound, if the NT is thickened, the risk of the fetus having Down syndrome, other chromosomal abnormalities, and congenital heart disease increases.
3. Non-Invasive Prenatal Genetic Testing
Non-invasive prenatal genetic testing is typically conducted between 12 and 22 weeks of gestation. Peripheral blood is collected from the pregnant woman, and next-generation DNA sequencing technology is used to sequence free fetal DNA fragments present in the maternal plasma. Bioinformatic analysis of the sequencing results enables the determination of the risk of the fetus having chromosomal aneuploidies such as Down syndrome. This method has a high accuracy rate for detecting Down syndrome.
4. Amniocentesis
Amniocentesis is usually performed between 16 and 22 weeks of gestation. Under ultrasound guidance, a needle is inserted through the pregnant woman's abdominal and uterine walls into the amniotic cavity to collect amniotic fluid. The amniotic fluid contains fetal cells that have been shed, and chromosomal karyotyping of these cells can directly detect whether the fetus has chromosomal numerical or structural abnormalities. This serves as an important criterion for diagnosing Down syndrome.
5. Cordocentesis
Cordocentesis is commonly performed after 20 weeks of gestation. Under ultrasound guidance, a needle is inserted through the pregnant woman's abdominal wall into the fetal umbilical cord to collect umbilical cord blood. The umbilical cord blood contains abundant fetal cells, which can undergo chromosomal karyotyping and genetic testing to definitively determine whether the fetus has Down syndrome.
Before conception, it is important to undergo comprehensive preconception checkups, including chromosomal testing for both partners, to understand one's health status. If there is a family history of genetic diseases or other high-risk factors, timely consultation with a doctor and appropriate interventions should be considered.
