Diagnosing down syndrome 9gag wiki


• HCG ( human chorionic gonadotropin). HCG is a hormone made by the placenta. In fact, very early in pregnancy, it’s the substance used to detect pregnancy in home pregnancy tests, since it also shows up in urine. HCG levels in the blood of women carrying babies with Down syndrome tend to be higher than average.

• PAPP-A (pregnancy-associated plasma protein A). Women with low blood levels of PAPP-A have an increased chance that their baby will have Down syndrome. Low levels of PAPP-A also may indicate an increased risk for intrauterine growth restriction, premature delivery, preeclampsia, and stillbirth.

Prenatal cell-free DNA screening (cfDNA). This relatively new blood test, which screens for certain chromosome problems such as Down syndrome (as well as trisomy 13 and trisomy 18) can be done as early as 10 weeks, according to the Mayo Clinic. The drawback of the test is that in one percent to five percent or more of blood samples, no results can be obtained, even after the test is repeated. In addition, cfDNA is costly. Still, it can be worth it for women who are at risk of having babies with Down syndrome—i.e., those who are 35 or older.

Karyotyping. As described above, this is an analysis of a baby’s genetic makeup that looks at the number of chromosomes under a microscope. Under normal circumstances, there are 46 chromosomes organized in 23 pairs. Chromosome pairs are numbered one through 23. In the case of Down syndrome, there is an extra chromosome in the 21 spot, meaning there are three of this particular chromosome. (This is why the clinical name for Down syndrome is trisomy 21.) A karyotype can be done using almost any type of cell. When a diagnosis is being confirmed after birth, for example, the cells usually are taken from a sample of the baby’s blood.

FISH testing. The acronym FISH stands for fluorescent in situ hybridization. FISH testing or FISH analysis is a relatively new technique that can determine how many copies of a particular chromosome a cell has using fewer steps than those that are necessary for karyotyping, which requires a sample to be cultured for seven to 1n days before it can be analyzed. The results from FISH analysis can be ready within about 12 hours. The disadvantage of FISH is that unlike karyotyping, it only can reveal if there is an extra chromosome 21. It doesn’t offer any information about the structure of the chromosomes, information that would be needed to identify Down syndrome as complete, mosaic, or translocation trisomy 21.

Amniocentesis. This test involves using a sample of amniotic fluid to create a karyotype. Amniocentesis is done between 15 weeks and 20 weeks of pregnancy. It involves inserting a long thin needle into a woman’s abdomen in order to extract a sample of fluid from the amniotic sac. This fluid contains skin cells that have sloughed off of the fetus. An ultrasound is used to help the doctor performing the test guide the needle safely into the uterus. The procedure is quick, though most women report feeling some discomfort and mild cramping. Amniocentesis is relatively safe: It carries a 1-in-400 risk of causing miscarriage. According to the National Down Syndrome Society (NDSS), the test is nearly 100 percent accurate in diagnosing Down syndrome prenatally. What’s more, it can distinguish between complete trisomy 21, translocation Down syndrome, and mosaic Down syndrome.

Chorionic villi sampling (CVS). As with amnio, CVS testing uses karyotyping to diagnose Down syndrome. However, the cells examined are taken from structures in the placenta called chorionic villi. CVS is performed at 11 to 13 weeks of pregnancy and is done in one of two ways: Either a needle is inserted directly into the abdomen or is threaded through the cervix (much like having a Pap smear). The insertion of the needle can be painful, but the procedure is very quick. CVS poses the same small risk of miscarriage as amnio, is nearly 100 percent accurate, and is able to reveal which type of trisomy 21 a baby has. Imaging

Ultrasound (sonogram) screening. Ultrasounds work by using sound waves too high for the human ear to hear to generate an image of the fetus. To do an ultrasound, your doctor will rub a special gel on your abdomen to make it slippery and then slide a transducer, a wand-like apparatus that transmit the sound waves into your abdomen, over your belly. These waves pose no risk to you or your child.

The sound waves travel through the amniotic fluid and bounce off of structures located in the uterus. These waves bounce back at different speeds depending on the density of the structures they hit before deflecting. A computer then turns these returning sound waves into an image of the fetus. The harder or denser a structure is, the brighter it will show up on the monitor.

Occasionally, but not always, infants with Down syndrome show subtle signs, called soft markers, on an ultrasound that suggest they may have Down syndrome. These signs do not mean that a baby has Down syndrome for sure. Further testing would need to be done to diagnose Down syndrome.

Duodenal atresia. This abnormality of the duodenum, a part of the small intestine, will show up on an ultrasound as a double bubble caused by extra fluid and swelling in the duodenum and stomach. Duodenal atresia sometimes may be detected as early as 18 to 20 weeks but usually isn’t seen until after 24 weeks. Another sign of duodenal atresia in pregnancy is excessive amniotic fluid. If a duodenal atresia shows up in an ultrasound, there is a 30 percent chance that the baby will have Down syndrome.

Nuchal translucency ultrasound screening. This specialized ultrasound measures the amount of fluid behind the baby’s neck, an area called the nuchal translucency. This is a specialized and difficult measurement to obtain, and the ultrasound can only be done by someone who has been specifically trained and certified on obtaining this measurement.

In general, a measurement under 3 millimeters (mm) is considered normal (or screen negative) and a nuchal translucency measurement of over 3 mm is considered abnormal or (screen positive). In this case, it will be important to meet with a genetic counselor to discuss your screening results, what they mean, and your diagnostic testing options such as CVS and amniocentesis.