Down syndrome is a chromosomal abnormality (a genetic disability) that leads to predictable physical and cognitive characteristics, such as certain facial features (almond-shaped eyes, protruding tongue, low ears), small hands with a single palmar fold, heart defects, hearing problems, learning disabilities and reduced IQ. It is also referred to as trisomy 21 because in the twenty-first pair of chromosomes there is an extra chromosome that causes the syndrome. Many parents want to know if their unborn child has Down syndrome, so there are several prenatal diagnostic and screening tests that can determine this.
Steps
Part 1 of 2: Undergo Screening Tests
Step 1. Go to the gynecologist when you are pregnant
Your pediatrician or family doctor can tell you if your baby has Down syndrome once born, but if you want to know first, ask for several screening tests. Prenatal ones can reveal if there is a high probability that the baby is affected, but they do not provide a perfect estimate.
- If the results show a high probability rate, the gynecologist recommends diagnostic tests to be sure.
- The American College of Obstetricians and Gynecologists recommends that all women (regardless of age) undergo screening exams.
- There are different tests that are carried out according to the month of pregnancy: in the first trimester the combined test, the integrated test and the free circulating fetal DNA take place.
Step 2. Undergo the combined test
It is performed in the first three months of pregnancy and has two phases: a blood test and an ultrasound. The blood test measures the levels of pregnancy-associated plasma protein A (PAPP-A) and human chorionic gonadotropin (HCG); abdominal ultrasound (completely painless) measures the nuchal area of the fetus and is called nuchal translucency.
- Abnormal concentrations of PAPP-A and HCG typically indicate something abnormal affecting the fetus, but not necessarily trisomy 21.
- The nuchal translucency test measures the amount of fluid in that area which, when abundant, is usually an indication of a genetic disability, which is not necessarily Down syndrome.
- The gynecologist takes into account your age (late pregnancies are more at risk), the results of blood tests and ultrasound to assess the odds of the fetus having the syndrome.
- Remember that these types of tests are not always performed; however, if you are over 35, your gynecologist may recommend them.
Step 3. Learn about the integrated test
It is performed in the first and second trimester (within the sixth month) and consists of two parts: the combined examination (blood test and ultrasound), which is done in the first trimester to assess the PAPP-A concentration and nuchal translucency, and another blood test, which monitors pregnancy-related hormones in addition to other substances.
- The blood test that takes place in the second trimester is also called a tritest and measures the levels of HCG, alpha-fetoprotein, unconjugated estriol and inhibin-A; abnormal outcomes indicate a fetal development problem or a genetic abnormality.
- In practice, it is a control test following the combined one and allows you to compare blood values.
- If the fetus has Down syndrome, you have high levels of HCG and inhibin-A coupled with low concentrations of alpha-fetoprotein and unconjugated estriol.
- The integrated test is reliable together with the combined test to establish the probability that the child is affected by the syndrome; however, it has a small false positive rate (a small number of women are mistakenly told that the fetus has trisomy 21).
Step 4. Evaluate free circulating fetal DNA analysis
It allows to control the genetic material of the fetus that circulates in the maternal blood. A blood sample is taken and tests are performed to look for anomalies; in general, the test is recommended for women who are at high risk of having a baby with the syndrome (over 40) and / or whose previous screening tests have revealed a high percentage of probability.
- The exam usually takes place around the 10th week of pregnancy.
- Free circulating fetal DNA analysis is much more specific than other screening tests; a positive result means there is a 98.6% chance that the fetus has trisomy 21, while a negative result means a 99.8% chance that the baby is healthy.
- If the test is positive, the gynecologist recommends more invasive tests, such as those described in the next section of the article.
Part 2 of 2: Undergo Diagnostic Tests
Step 1. Contact your gynecologist
If he recommends diagnostic tests, it means that he fears that there is a good chance that your child has trisomy 21; his fear is based on the results of previous screening tests and on your age. Although these prenatal tests can determine the presence of the syndrome, they carry a greater risk to your health and that of the fetus, because they are more invasive; consequently, you need to evaluate its advantages and disadvantages with the gynecologist.
- During these procedures, a needle or other similar instrument is inserted into the abdomen and uterus to take a sample of fetal fluid or tissue for laboratory analysis.
- The prenatal diagnostic tests that are able to identify with certainty trisomy 21 in the fetus are: amniocentesis, CVS and umbilical cord blood sampling. However, remember that these procedures are not without risks; in fact, bleeding, infection and damage to the fetus can develop.
Step 2. Undergo amniocentesis
This involves taking a sample of amniotic fluid that surrounds the developing baby. A long needle is inserted into the uterus (through the lower abdomen) to aspirate fluid which also contains fetal cells; the chromosomes of these cells are then analyzed for trisomy 21 or other genetic abnormalities.
- Amniocentesis is performed in the second trimester of pregnancy, between the fourteenth and twenty-second weeks.
- The greatest risk is miscarriage and fetal death, which increases when amniocentesis is performed before the fifteenth week.
- The chances of miscarriage caused by the examination are around 1%.
- Thanks to this test it is also possible to distinguish the different forms of Down syndrome: regular trisomy 21, mosaicism and Robertsonian translocation.
Step 3. Evaluate CVS
In this case, a sample of chorionic villi - the embryonic part of the placenta (which surrounds the fetus in the uterus) - is taken and analyzed for abnormalities in the number of chromosomes. This procedure also involves the insertion of a needle into the abdomen and uterus, it is performed in the first trimester between the ninth and eleventh week, although it is considered less risky once the first ten months have elapsed. CVS is performed before amniocentesis, an important detail if you decide to terminate the pregnancy if the fetus is affected by the syndrome.
- CVS carries a slightly higher risk of miscarriage than amniocentesis that is performed in the second trimester (slightly more than 1%).
- Also this test allows to recognize the different forms of the syndrome.
Step 4. Be very careful with umbilical cord blood sampling
This test, also called cordocentesis, involves taking a blood sample from the umbilical cord vein by inserting a long needle into the uterus. The blood is then analyzed for genetic mutations (extra chromosomes); it takes place towards the end of the second quarter, between the eighteenth and twenty-second weeks.
- It is the most accurate test for diagnosing Down syndrome and can confirm the outcomes of amniocentesis or CVS.
- However, it carries much greater risks of miscarriage than other diagnostic tests; consequently, the gynecologist should only recommend it if you have so far obtained inconclusive results.
Step 5. Proceed with postnatal diagnosis
If you did not undergo screenings or diagnostic tests during gestation, the process of determining if the baby has trisomy 21 usually takes place with an examination of the appearance of the little patient. Sometimes, however, some newborns show aesthetic characteristics similar to those predicted by the disease, even if they are completely healthy; as a result, the pediatrician may request a test called a karyotype study.
- The test involves a simple sample of the child's blood and the sample is analyzed for the extra chromosome in the twenty-first pair, which is present in all or only some cells.
- A good reason why prenatal tests (diagnostic and screening) are performed promptly is to allow parents the opportunity to make choices, including termination of pregnancy.
- If you feel you are unable to care for a newborn with Down syndrome, ask your gynecologist about your options for giving him up for adoption.
Advice
- Newborns with Down syndrome have a life expectancy of 40-60 years, which is significantly longer than that of previous generations.
- This is the most common chromosomal abnormality and affects one in 700 children.
- Screening blood tests that are performed during the first and second trimester of pregnancy can only predict 80% of cases.
- Nuchal translucency testing is usually done between the 11th and 14th week of gestation.
- If you are considering in vitro fertilization, know that genetic tests are done for the syndrome before implantation.
- Knowing early in pregnancy that your newborn suffers from trisomy 21 allows you to better prepare yourself.
