What is the test for Down's syndrome?
How to Test for Down Syndrome
Down syndrome is a chromosomal abnormality (genetic disability) in babies that leads to predictable mental and physical characteristics, such as certain facial features (slanted eyes, thick tongue, low-set ears), small single-creased hands, heart defects, hearing problems, learning disabilities and reduced intellect.It's also called trisomy 21 because an extra chromosome attaches to the 21st pair to cause the disability. Many parents want to know if their unborn child has Down syndrome, so there are different types of prenatal screenings and diagnostic tests that can be done to determine it.
Getting Screening Tests for Down Syndrome
See your doctor while you're pregnant.Your doctor or pediatrician can tell you if your child has Down syndrome once they are born, but if you want to know beforehand, ask about the various types of screening tests. Prenatal screening tests can show if there is an increased likelihood your unborn baby has Down syndrome, but they are not a perfect estimate.
- If a prenatal screening test shows an increased likelihood your baby has Down syndrome, then your doctor will recommend a diagnostic test to be more certain.
- The American College of Obstetricians and Gynecologists recommends that all women (regardless of age) get screening tests for Down syndrome.
- There are different screening tests related to how far along you are in your pregnancy and include: the first trimester combined test, the integrated screening test and the cell-free fetal DNA analysis.
Get the first trimester combined test.The first trimester combined test is done within the first 3 months of pregnancy and involves two steps: a blood test and an ultrasound exam.The blood test measures levels of PAPP-A (pregnancy-associated plasma protein-A) and HCG (human chorionic gonadotropin) hormone being produced in your body. (HCG). In addition, a painless ultrasound exam is used on your abdomen to measure an area on the back of the fetus's neck called the nuchal translucency.
- Abnormal levels of PAPP-A and HCG typically indicate something unusual with your baby, but not necessarily Down syndrome.
- The nuchal translucency screening test measures the amount of fluid that's collected there. Abnormally high amounts of fluid usually indicates a genetic disability, but not just Down syndrome.
- Your doctor will consider your age (older equals higher risk), the results of the blood test, and the ultrasound images to decide if it's likely your fetus has Down syndrome.
- Just keep in mind that these types of tests are not done in every instance of pregnancy. However, if you are over 35, then you are at higher risk of having a baby with Down syndrome and your doctor may recommend testing.
Ask about the integrated screening test.The integrated screening test is done during the first and second trimesters of pregnancy (within the first 6 months) and consists of 2 parts: a combined blood / ultrasound screening done in the first trimester looking at PAPP-A levels and nuchal translucency (as described above) and a more thorough blood test looking at pregnancy-related hormones and other substances.
- The second trimester blood test, called the "quad screen", measures levels of HCG, alpha fetoprotein, estriol and inhibin A in your body. Abnormal levels indicate a developmental or genetic problem in your baby.
- This test is essentially a follow-up to the first trimester combined test, as it adds a second trimester comparison blood test.
- If you're carrying a baby with Down syndrome, you'll have higher levels of HCG and inhibin A, but lower levels of alpha fetoprotein (AFP) and estriol.
- The integrated screening test is as reliable as the first trimester combined test in estimating the likelihood of Down syndrome, but it has fewer false-positives — less women are told incorrectly they're carrying a Down syndrome child.
Consider the cell-free fetal DNA analysis.The cell-free fetal DNA test checks for your baby's (fetal) DNA material that's circulating in your blood.A blood sample is taken and the genetic material is analyzed for abnormalities. This test is usually recommended if you're at high risk for Down syndrome (older than 40 years) and/or have an abnormal result in another type of screening test.
- For this screening test, your blood can be analyzed during pregnancy after about 10 weeks.
- The cell-free fetal DNA analysis is much more specific than other screening tests for Down syndrome. Apositiveresult means there's a 98.6% chance that your baby has Down syndrome, whereas a "negative" result means there's a 99.8% chance your baby doesn't.
- If this DNA screening test is positive, then your doctor will recommend a more invasive diagnostic test to confirm Down syndrome (see below).
Getting Diagnostic Tests for Down Syndrome
Consult with your doctor.If your doctor recommends a diagnostic test, it means they think you're at high risk for Down syndrome based on the results of screening test(s) combined with your age. However, although a prenatal diagnostic test can determine the presence of Down syndrome with certainty, they carry a higher risk to your health and that of your baby's because they are more invasive.As such, consult with your doctor about the pros and cons of such testing.
- Invasive testing means that a needle or similar implement must be inserted into your abdomen and uterus to take a sample of fluid or tissue in order to analyze it.
- Diagnostic tests that can positively identify Down syndrome in pregnant women include: amniocentesis, chorionic villus sampling (CVS) and cordocentesis. However, keep in mind that these procedures do not come without risks. There is a risk of bleeding, infection, and harm to the fetus.
Get an amniocentesis done.An amniocentesis involves collecting a sample of amniotic fluid that surrounds your growing baby. A long needle is inserted into your uterus (through your lower abdomen) in order to withdraw fluid that contains some cells from your baby.The chromosomes of the cells are then analyzed, looking for trisomy 21 or other genetic disabilities.
- An amniocentesis is usually performed during the second trimester, between weeks 14 to 22 of pregnancy.
- The main risk of amniocentesis is a miscarriage and death of the baby, which increases if it's done before 15 weeks.
- The risk of a spontaneous termination (miscarriage) from amniocentesis is estimated at 1%.
- Amniocentesis can also distinguish between the slightly different forms of Down syndrome: regular trisomy 21, translocation Down syndrome and mosaic Down syndrome.
Consider chorionic villus sampling (CVS).In a CVS procedure, cells are taken from a part of the placenta (which surrounds your baby within your uterus) called the chorionic villus and used to analyze the chromosomes for an abnormal number.This test also requires inserting a large needle into your abdomen / uterus. CVS is usually performed in the first trimester, between 9 to 11 weeks of pregnancy, although after the 10th week is considered less risky. This test be done sooner than amniocentesis, which is important if you plan to abort the baby if it has Down syndrome.
- A CVS carries a slightly higher risk of miscarriage than a second trimester amniocentesis — perhaps slightly more than a 1% chance of miscarriage.
- A CVS can also distinguish between the slightly different genetic forms of Down syndrome.
Be very cautious with cordocentesis.With cordocentesis, also called percutaneous umbilical blood sampling or PUBS, fetal blood is taken from a vein in the umbilical cord through the uterus with a long needle and examined for genetic mutations (extra chromosomes).This diagnostic test is performed later in the second trimester, between 18 to 22 weeks of gestation.
- A cordocentesis is the most accurate diagnostic method for Down syndrome and can confirm the results from an amniocentesis or CVS procedure.
- PUBS carries a much greater risk of miscarriage than amniocentesis or CVS, so your doctor should only recommend it if results from other diagnostic tests are unclear.
Diagnose your newborn.If you didn't get any prenatal screening or diagnostic tests done prior to giving birth, then the initial diagnosis of Down syndrome is typically based on your baby's appearance.However, some babies may have the general appearance of Down syndrome, but not have the condition, so your doctor can order a test called chromosomal karyotyping.
- A chromosomal karyotype requires a sample of your baby's blood to analyze for an extra 21st chromosome, which can be present in all or some cells.
- A significant reason for early screening and diagnostic tests is to give parents options before birthing, including terminating the pregnancy.
- If you believe you will be unable to care for your newborn with Down syndrome, ask your doctor about adoption options.
QuestionCan I detect it before the first trimester is over?MindfulyEliCommunity AnswerYes, you can detect down syndrome during the first semester. This is done via blood tests and ultrasounds.Thanks!
QuestionWhat are the signs of Down syndrome?wikiHow ContributorCommunity AnswerDown Syndrome is a genetic disability that causes developmental delays and a unique appearance. People with Down Syndrome tend to be short and stocky in stature, with a small nose, slanted eyes, and small ears. They may learn to speak at a later age (or not at all) and use sign language in the interim. They tend to have difficulty with speech, motor skills, and intellectual tasks. People with Down Syndrome are often more loving, friendly, and optimistic in nature. They can be wonderful family members, friends, romantic partners, and loved ones in general. For more, read How to Recognize the Signs of Down Syndrome.Thanks!
QuestionCan I know the references for this article?Top AnswererAll sources that were used in the creation of the article can be found by scrolling all the way down, past the "Related Wikihows" to "Sources and Citations."Thanks!
- Babies born with Down syndrome can now expect to live between 40-60 years, which is significantly longer compared to previous generations.
- Down syndrome is the most common chromosomal abnormality and occurs in about 1 in in every 700 births.
- Blood screening tests done in the first and second trimesters are only able to predict about 80% of babies with Down syndrome.
- The nuchal translucency test is typically done when you're between 11-14 weeks pregnant.
- If you're considering in vitro fertilization, a preimplantation genetic diagnosis can be done for Down syndrome before the embryo is implanted.
- Learning early in your pregnancy that your baby has Down syndrome allows you to better prepare for it.
Video: Advances in Non-invasive Prenatal Testing
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