Down syndrome screening: an important prenatal check-up item during pregnancy

Down syndrome screening is a method of prenatal testing that uses blood tests and ultrasound to assess the risk of a fetus having Down syndrome (trisomy 21) and other chromosomal abnormalities. The main content includes early screening (11-13 weeks of pregnancy) and mid-term screening (15-20 weeks of pregnancy). The risk value is comprehensively calculated by analyzing maternal serum markers (such as β-hCG, AFP, etc.) and fetal nuchal translucency thickness (NT value). Its core purpose is to provide pregnant women with scientific evidence to help them decide whether further diagnostic testing (such as amniocentesis) is needed. Screening results are divided into high risk, borderline risk and low risk, and should be dealt with appropriately based on doctor's advice.

Specific examination methods and times for Down syndrome screening

Down syndrome screening is usually divided into two stages: early screening is performed at 11-13 weeks of pregnancy, andB-ultrasound measurement of fetal nuchal translucency (NT) thicknessThe risk is assessed based on pregnancy-related protein (PAPP-A) and free β-hCG levels in the blood of pregnant women; mid-term screening is performed at 15-20 weeks of pregnancy and mainly detects PAPP-A in the blood of pregnant women.Alpha-fetoprotein (AFP), free estriol (uE3) and chorionic gonadotropin (hCG)and other indicators. Both screenings can use algorithms to generate risk values ​​based on maternal age, weight, gestational age and other factors. It should be noted that Down syndrome screening isrisk assessmentRather than confirming the diagnosis, high-risk results require further confirmation through amniocentesis or non-invasive DNA testing.

Interpretation of screening results and next steps

Down syndrome screening reports usually present the risk value in the form of a ratio (such as 1/1000). If the result is lower than the critical value (such as 1/270), the risk is low, and if the result is higher than the critical value, the risk is high. Critical risk requires clinical judgment. For high-risk pregnant women, your doctor may recommendNon-invasive prenatal genetic testing (NIPT)oramniocentesisto confirm the diagnosis. It should be noted that screening has a false positive rate (about 5%), so the results need to be viewed rationally. In addition, if the pregnant woman is ≥35 years old and has a family history of chromosomal abnormalities, diagnostic testing may be recommended directly, skipping the screening step.

Limitations and considerations for Down syndrome screening

Although Down syndrome screening can cover 60%-90% of Down syndrome cases, it cannot detect all chromosomal abnormalities or structural malformations. Its accuracy is affected by factors such as gestational age calculation error and maternal weight. You need to be fasting before the examination, and provide accurate information such as menstrual history and previous pregnancy history. Currently commonly used in ChinaDouble or triple screening, some areas have promoted quadruple screening (adding inhibin A testing). The cost is usually 200-500 yuan depending on the region, and some medical insurance can reimburse it. It should be clear that abnormal screening results do not mean that the fetus is definitely sick, and excessive anxiety needs to be avoided.

Summary: scientific cognition, rational choice

Down syndrome screening is an important prenatal and postnatal care method that provides a preliminary assessment of fetal health in a simple and non-invasive way. Pregnant women should follow the doctor’s advice to complete the examination at the appropriate gestational age and fully understand its"Screening" nature, to avoid equating risk values with diagnostic results. For high-risk groups, genetic experts should be consulted in a timely manner and follow-up examination plans should be selected based on their own circumstances. With the advancement of technology, new methods such as non-invasive DNA testing are gradually becoming popular, but traditional Down syndrome screening is still the first choice for most pregnant women because of its economy and universality.

Quote sources:
1. "Guidelines for Pre-Pregnancy and Pregnancy Health Care (2022)" by the Obstetrics and Gynecology Branch of the Chinese Medical Association
2. American College of Obstetricians and Gynecologists (ACOG) Practice Bulletin No. 226 (2020)
3. Product examples: Roche Diagnostics (Elecsys series chemiluminescence immunoassay analyzers), PerkinElmer (DELFIA screening system)
4. Data reference: WHO "Global Report on the Prevention and Treatment of Birth Defects" (2021)