Pregnant women aged 35 years and over should undergo Tangscreen testing between 16 and 18 weeks of pregnancy. The target diseases of the Tangscreen are primarily trisomy 21 syndrome, also known as Down syndrome, trisomy 18 syndrome, and open neural tube defects. The screening indicators for Tangscreen are free estriol, alpha-fetoprotein, and human chorionic gonadotropin (HCG). These three tests are biochemical indicators used to determine the risk of chromosomal abnormalities in the fetus. If any of these indicators exceed the normal standard values, it is considered high risk.

For individuals with a high risk of Tangscreen, further prenatal examinations should be conducted, including chromosomal karyotype analysis by amniocentesis, which is the gold standard for diagnosing fetal chromosomal diseases. If there are contraindications to amniocentesis, fetal DNA testing in maternal peripheral blood can also be performed, which can more accurately screen for chromosomal abnormalities in the fetus.

The Tangscreen test is a screening examination for the risk of fetal trisomy 18 syndrome, trisomy 21 syndrome, and developmental abnormalities of the fetal neural tube. After the delivery of a baby with trisomy 18 or 21 syndrome, there is a possibility of developmental disorders similar to those found in deaf and mute schools. And these two chromosomal abnormalities are the most common types of chromosomal abnormalities. Therefore, it is recommended that pregnant women undergo blood tests for Tangscreen between 11-13 weeks of amenorrhea and 16-18 weeks of pregnancy.

The Tangscreen test is used to screen for trisomy 21, trisomy 18, and neural tube defects by taking blood during pregnancy. The Tangscreen is divided into early, intermediate, and mid-trimester screenings, with early screening conducted between 11 and 13 weeks of pregnancy plus 6 days, and mid-trimester screening generally starting after 15 weeks of pregnancy. The Tangscreen is a preliminary screening for the incidence of Down syndrome within the population, and if the Tangscreen indicates a high risk or is at the critical value for high risk, further invasive DNA testing or amniocentesis may be required for a definitive diagnosis.