I am afraid that Down syndrome is one of the few congenital disorders that are familiar to even non-medical professionals. Many mothers are also worried about it, either because they don’t know if there is a need for testing or because they don’t know much about the risks it poses, so it’s difficult to make the right decision. Down syndrome can occur in every fetus, but the most critical influencing factor is the age of the mother. The older the mother, the greater the chance of the child developing Down syndrome. But because younger mothers are in the majority, 80 percent of Down syndrome children are born to mothers younger than 25. The chance of a mother having Down syndrome if she is younger than 25 is 1 in 1,250; at age 30 it is 1 in 1,000, at age 35 it is 1 in 400, and at age 40 it is 1 in 100; a mother at age 45 has as much as a 1 in 30 chance of conceiving a child with Down syndrome. In the 1980s, the average life expectancy of a child with Down syndrome was only 25 years. But with advances in medicine, the average life expectancy for someone with Down syndrome is now 60 years. There isn’t a mother who doesn’t want a healthy child. Because there is no way to reverse Down syndrome once it is present, early detection is crucial. So how can you know if your child has Down syndrome while inside the mother’s womb? Relying on pulse cutting is definitely not an option. The good thing is that modern medicine already has accurate and effective means to know in advance. There are two types of tests to detect Down syndrome: screening tests and diagnostic tests. Screening tests, as the name suggests, screen for the possibility of Down syndrome. Once an abnormality is detected, or if you are a high-risk pregnancy yourself, a diagnostic test to confirm the diagnosis is required. Screening tests include a blood test and an ultrasound. These two tests do not harm the mother or the child and are very safe. However, the disadvantage is that they only provide a risk assessment and cannot diagnose with certainty whether the child has Down syndrome or not. The blood test measures the concentration of proteins in the blood. Certain proteins are elevated in the mother of a child with Down syndrome and can indicate Down syndrome. Depending on the results of the test, and taking into account the age of the pregnant woman, a screening test can give an approximate likelihood of having Down syndrome, which tells about 79-90% of the chance of risk. This also means that there is about a 21% chance of being missed. Therefore if there is a high risk, diagnostic tests are needed to determine it. The American College of Obstetricians and Gynecologists recommends that all pregnant women undergo screening tests, regardless of age. Of course, this is only a recommendation, not a mandate, and you need to make your own judgment as to whether or not to do it. A blood test and fetal nuchal ultrasound are usually recommended early in pregnancy, between 11 and 13 weeks. This ultrasound measures the thickness of the fetal nuchal translucency band, which exceeds a certain thickness to indicate the possibility of Down syndrome. Alternatively, a blood test without the ultrasound may be done only in the second trimester, at 15 to 20 weeks. This blood test detects a number of additional proteins and works in the same way. Which one you choose depends on factors such as age and family history. If the screening test reveals a higher risk of Down syndrome, a decision needs to be made about whether or not to have a diagnostic test. This is because, as stated above, screening tests do not confirm the diagnosis. Diagnostic tests include amniocentesis and chorionic villus biopsy. These two tests have a very high rate of confirming the diagnosis, which can be over 99%. So the presence or absence of Down syndrome is basically determined by these two tests. Therefore the American College of Obstetrics and Gynecology also recommends that pregnant women, regardless of age, can opt out of the screening tests and go straight to the diagnostic tests. Prior to this it was only recommended that pregnant women over the age of 35, or those at increased risk, have the diagnostic test done because of the risks associated with the diagnostic test. Amniocentesis is a procedure where a needle is inserted into the uterus and a bit of amniotic fluid is withdrawn for testing, and is usually performed at 16 to 20 weeks. Chorionic villus biopsy takes some placental tissue directly to check for chromosomal abnormalities and is usually done at 11 to 14 weeks. These two tests are very accurate but because they are invasive, there are inevitable risks. How high are the risks? The chance of miscarriage due to amniocentesis varies depending on the hospital, but the average is about less than 1/300~1/500, which is very low. Chorionic villus biopsy has a slightly higher risk, about 1/100~1/200, because some live tissue has to be taken. What are the factors to be considered? 1. Screening results. 2. Increased risk if there is a previous history of carrying a child with Down syndrome. 3. Family history. 4, Age. Despite all this, the choice of which test to do is a matter of your own judgment and decision based on understanding the pros and cons of these tests and evaluating the level of risk based on your own situation. Usually after the screening tests are done, your doctor can tell you an approximate risk rate. Anything above 1/150, such as 1/100, which means there is a 1/100 chance that your child will have Down syndrome, is usually considered high risk; anything below 1/150 is low risk.