Why do doctor's mainly test for down syndrome? Aren't there 26 chromosones that could lead to abnormalities?

Question

Are the others not as common?

Answer 1

Trisomy 21 is one of the few trisomies that will lead to a live birth.  Most of the others will miscarry, so testing isn't necessary, as the pregnancy will not survive long.

Answer 2

They can actually test for just about any genetic disorder, especially ones that tend to run in families.  Down syndrome is a common test done during pregnancy because it is one of the most common genetic disorders, and because it can cause heart problems, which can be treated better and more quickly if the doctor is aware of them before the baby's birth.  They also test for spina bifida and other congenital abnormalities.  The rate of mutation in each chromosome is different, and the trisomy 21 syndrome which causes Down syndrome happens to be one of the common ones.  Hope that helps!

Answer 3

Trisomy 21 causes downs syndrome. Its a tripling of the 21st chromosome.  Downs syndrome is probably checked because it is common and it is easily detectible.

Answer 4

There are 23 pairs of chromosomes, including the s*x (x and y) chromosomes. Down syndrome happens when there is an extra 21st chromosome (3 in all). The 21st is the smallest chromosome, so having an extra one causes the fewest problems. If any of the other pairs have an extra one, the baby usually doesn't survive and miscarries because there are so many problems. Some babies with an extra 18th chromosome survive to birth, but most die soon after. Babies with an extra s*x chromosome can also survive.

There are also lots of other genetic problems that don't involve entire chromosomes, but they are harder to detect and more rare so they don't test in advance for those, unless there's a reason, like some other abnormality showing up that is a symptom of that problem.

Answer 5

Down syndrome is the most frequent of the chromosomal anomalies, occurring more often that any other chromosomal defect. A group of tests known as Triple Screen or Quadruple Screen is used to screen for Down syndrome. (A screening test separates a high-risk person from a lower risk population, it is not diagnostic in itself.)

Testing for other chromosomal anomalies may be indicated by family history, history of a previously affected infant, a parent who is a balanced or unbalanced carrier of an abnormal piece of chromosomal material. Or, certain abnormalities on a prenatal ultrasound may indicate a chromosomal anomaly.

Many fetuses with abnormal chromosomes spontaneously abort, but many survive, often with severe defects.