How to perform Down syndrome screening
May 20, 2025
Source: Cainiu Health
Dr. Zhang Lu
Introduction
Draw maternal peripheral blood for testing. Measure whether fetal alpha-fetoprotein, human chorionic gonadotropin (hCG), free β-hCG, unconjugated estriol, and inhibin A are within normal ranges. This test is generally performed between 12 and 22 weeks of pregnancy. The method has requirements regarding maternal weight and age, with an accuracy of approximately 60%-70%. False positives and false negatives are possible.
Generally, Down syndrome screening can be performed using methods such as maternal serum screening, non-invasive DNA testing, amniocentesis, chorionic villus sampling (CVS), and nuchal translucency thickness measurement. Details are as follows:
1. Maternal Serum Screening: This test involves drawing blood from the mother's peripheral circulation to measure levels of fetal alpha-fetoprotein (AFP), human chorionic gonadotropin (hCG), free β-hCG, unconjugated estriol (uE3), and inhibin A to determine whether they fall within normal ranges. It is usually performed between 12 and 22 weeks of pregnancy. This method has certain requirements regarding maternal weight and age, with an accuracy rate of approximately 60%-70%. There is also the possibility of false-positive or false-negative results.
2. Non-Invasive DNA Testing: This method involves drawing blood from the pregnant woman's peripheral circulation to perform next-generation sequencing on fetal DNA fragments circulating in the maternal bloodstream. It can assess the risk of the fetus having trisomy 21 and other chromosomal abnormalities. There is no specific time restriction, although it is generally recommended during pregnancy. Women over age 40 or those exceeding certain weight limits may not be suitable candidates for this test.
3. Amniocentesis: In this procedure, a needle is guided by ultrasound through the abdominal wall and uterine wall into the amniotic cavity to extract an appropriate amount of amniotic fluid for testing. It can detect fetal infections and chromosomal abnormalities, and fetal metabolic abnormalities can also be assessed by analyzing amniotic fluid metabolites. It is generally recommended between 17 and 23 weeks of pregnancy. The procedure should be performed under a physician's guidance, and maternal health should be closely monitored afterward.
4. Chorionic Villus Sampling (CVS): This method involves inserting a thin needle under ultrasound guidance to the placental area to collect chorionic villi samples for testing. It can be performed transcervically or transvaginally. Fetal chromosomal abnormalities can be identified by analyzing the genetic material in the chorionic villi. It is typically performed early in pregnancy. The procedure should be conducted under a physician's guidance, and maternal health should be closely monitored afterward.
5. Nuchal Translucency Thickness Measurement: Nuchal translucency measurement is an ultrasound examination performed early in pregnancy. By measuring the maximum thickness of the fluid-filled space at the back of the fetal neck, it can assess the risk of chromosomal abnormalities. If the nuchal translucency measurement exceeds the normal range, further diagnostic testing may be required.
Prior to undergoing any screening, it is important to consult with a physician.
