Is Down’s syndrome screening mandatory? How is it done? The majority of regions currently offer mid-trimester Down’s syndrome screening, which is usually done at 15 to 20 weeks of gestation, where blood is taken from the pregnant woman for HCG (human chorionic gonadotropin), uE3 (free estriol), AFP (alpha-fetoprotein), and ihA (inhibin A) tests to calculate the risk of the fetus having a chromosomal abnormality by calculating levels in the general population. When is Down’s syndrome screening done? Do I have to fast? There are two types of screening tests: early and mid-term screening. Early screening is performed at 11-14 weeks and is performed in fewer hospitals because it requires a combination of imaging and serological tests and is more costly. Many pregnant mothers ask if fasting is required. The screening does not require fasting, because there is no relationship between the blood tests for HCG, uE3 and AFP and whether to eat or not. What is the purpose of Down’s syndrome screening? Down’s syndrome screening is mainly to screen the fetus for chromosome aneuploidy abnormalities, which seems quite complicated. Down’s syndrome screening is mainly for chromosome 21, chromosome 18 and open spina bifida. Once these abnormalities are confirmed, it may be necessary to discuss whether to abandon the pregnancy. How accurate is Down’s syndrome screening? Just like the name of Down’s syndrome screening, it’s a screening! In our hospital, for example, JMC performs a triple screen, which examines the pregnant woman’s blood for HCG, AFP and uE3. With a false-positive rate of 5%, the triple serologic screen can screen for Down syndrome in 69% of cases, and the quadruple serologic screen can screen for 81% of detections. In other words, this is only a screening test, the accuracy rate is not particularly high, and if the risk is high, further tests may be needed to confirm the diagnosis. Is the fetus safe if the result of Down’s syndrome screening is low risk? If your test result is low risk, then first of all, congratulations, your baby is basically safe, but there is still a very low chance of Down’s syndrome, because there are many correlations between Down’s screening and the week of pregnancy, such as miscalculation of the week of pregnancy, laboratory errors, abnormal kits, etc., which may cause low risk but actually have problems. If there is no abnormality in the screening ultrasound, the fetus is basically safe. What is the next step if the screening result is high risk? If the test results indicate a high risk, the first thing to do is to analyze the test results to see if there is a miscalculation of the gestational week. If the gestational week is verified to be correct, then prenatal diagnosis is generally recommended for high risk. Amniocentesis is performed by extracting the free fetal cells from the amniotic fluid of the pregnant woman for chromosomal examination to confirm or exclude fetal chromosomal abnormalities. The other method is to take the blood of the pregnant woman and sequence the free DNA inside to predict the chance of fetal chromosomal abnormalities.