Down’s syndrome is one of the few congenital disorders that even non-medical professionals are familiar with. Many mothers are worried about it, because they do not know whether it is necessary to be tested, and because they do not know much about the risks it poses, and they do not trust their doctors, so it is difficult to make the right decision. What is Down’s syndrome? Down syndrome is a condition caused by congenital chromosomal abnormalities in the fetus. There are many congenital disorders caused by chromosomal abnormalities, and Down syndrome is one of the most common. Chromosomes are tiny ribbon-like structures that carry genetic information within our body cells. A normal human cell has 46 chromosomes, each two of which come together in a pair, for a total of 23 pairs. Twenty-three of these come from the mother’s egg and the other 23 come from the father’s sperm. When the sperm and egg combine in the mother’s body to form a fertilized egg, it is laid in the uterus, which means it is planted, takes root, and then begins to grow rapidly like a sapling. The fertilized egg changes from one to two, two to four, and four to eight, until it becomes a mature fetus. During this division, the chromosomes inside the cell have to replicate themselves, become double, and then divide again, so there should still be the correct 23 pairs of chromosomes inside each new cell. However, as you can imagine, this process of replication and division goes round and round and is repeated countless times, it is inevitable that once something goes wrong, big or small. When an error occurs, the wrong chromosome appears, and the cell still replicates the wrong chromosome. In this way, the normal chromosome is replaced by the error, normal cell function is disrupted, and the disease caused by the chromosomal abnormality emerges. In the 1980s, the average life expectancy of a child with Down syndrome was only 25 years. But with medical advances, the average life expectancy of a person with Down syndrome is now 60 years. There is not a mother who does not want a healthy child. Because there is no way to reverse Down syndrome once it appears, early detection is crucial. So how can you know if your child has Down syndrome while still inside the mother’s tummy? There are two types of tests to detect Down syndrome: screening tests and diagnostic tests. 1. Screening test, as the name suggests, is to screen for the possibility of Down syndrome. Once an abnormality is found, or if you are a high-risk pregnant woman, a diagnostic test to determine the diagnosis is required. The screening test consists of a blood test and an ultrasound. These two tests are not harmful to the mother or child and are very safe. However, the disadvantage is that they only provide a risk assessment and do not provide a definitive diagnosis of whether the child has Down syndrome or not. The blood test is a test for the concentration of proteins in the blood. Certain proteins are elevated in the mother of a child with Down syndrome, which can also indicate Down syndrome. Depending on the results of the test, and taking into account the age of the mother, the screening test can give an approximate likelihood of having Down syndrome, telling about a 79-90% chance of risk. This also means that there is about a 21% chance of being missed. Therefore, if there is a high risk, a diagnostic test is needed to determine this. The American College of Obstetrics and Gynecology recommends that all pregnant women receive a screening test, regardless of age. Of course, this is a recommendation, not a mandate, and it is up to your own judgment whether to do it or not. Blood tests and a fetal nuchal ultrasound are usually recommended in early pregnancy, 11 to 13 weeks. This ultrasound measures the thickness of the fetal nuchal translucency, above which a certain thickness indicates the possibility of Down’s syndrome. Alternatively, a blood test without ultrasound may be done only in the second trimester, from 15 to 20 weeks. This blood test detects more proteins and is based on the same principle as above. Which one to choose depends on factors such as age and family history. 2. If the screening test reveals a high risk of Down syndrome, it is time to decide whether to do a diagnostic test. Because as mentioned above, the screening test cannot confirm the diagnosis. Diagnostic tests include amniocentesis and chorionic villus biopsy. These two tests have a very high rate of confirmation, reaching over 99%. So the presence or absence of Down syndrome can be basically determined by these two tests. Therefore the American College of Obstetrics and Gynecology also recommends that pregnant women, regardless of their age, may choose to skip the screening test and go directly to the diagnostic test. Until then it is only recommended that pregnant women over the age of 35, or those at increased risk, have a diagnostic test because of the risks associated with diagnostic tests. Amniocentesis is performed by using a needle to puncture into the uterus and draw out a little amniotic fluid for testing, and is usually performed at 16 to 20 weeks. A chorionic villus biopsy directly removes some placental tissue to check for chromosomal abnormalities and is usually performed at 11 to 14 weeks. These two tests are highly accurate but inevitably carry risks because they are invasive. How high is the risk? The chance of miscarriage due to amniocentesis varies depending on the hospital, but the average is about less than 1/300 to 1/500, which is very low. Chorionic villus biopsy has a slightly higher risk, about 1/100 to 1/200, because some biopsies have to be taken. Although so much has been said, you have to make your own judgment and decision on which test to do, based on understanding the pros and cons of these tests and assessing the level of risk according to your own situation. Usually after the screening test is done, your doctor can tell you an approximate risk rate. Anything above 1/150, such as 1/100, which means there is a 1 in 100 chance that your child will have Down syndrome, is usually considered high risk; anything below 1/150 is low risk.