Down syndrome tests

I thought some might be interested in how doctors test for whether a pregnant mother has a kid with "chromosomal abnormalities." Of course, the allusion here is primarily but not solely to a child with Down syndrome (e.g. doctors can also look for other things like anencephaly or spina bifida).

Some stats

Approximately 85%-90% of pregnancies diagnosed with Down syndrome end up with the parent(s) terminating the pregnancy. I don't currently have the stats for what percentage of Down syndrome abortions make up all abortions. Maybe someone else can weigh in.

Anyway, these tests are routine tests. Commonly accepted practice. Doctors aim to run these tests for every single pregnancy. It's estimated about 3/4ths of all pregnant women actually do undergo these tests.

Four tests

There are four tests. Two of the tests are screening tests, while the other two tests are diagnostic. Also, two of the tests are done in the first trimester (between 10 and 13.5 weeks). And the other two tests are performed during the second trimester. In other words, there is one screening test and one diagnostic test in the first trimester, and there is one screening test and one diagnostic test in the second trimester. There are other tests but these are the more common ones from what I understand.

First trimester tests

1. Nuchal translucency test. This is a screening test. Ultrasound is used to see how thick the nape of the neck of the baby is. If it's a certain thickness, due to fluid around the neck, the baby is likely to have Down syndrome.



2. Chorionic villus sampling test. This is a diagnostic test. A needle or tube via either the abdomen or via the vagina is used to collect cells from the pregnant woman's placenta and tested.



Second trimester tests

1. Triple test. This is a screening test. The mother's blood is drawn and tested for three things - AFP (a protein produced by the baby), hCG (a hormone produced by the placenta), and estriol (a hormone produced by the baby and placenta.

2. Amniocentesis test. This is a diagnostic test. A needle is inserted via the woman's abdomen in order to reach the amniotic sac surrounding the baby, and a sample of the fluid in this sac is taken and tested.



Reliability and risks

Each of these tests are reliable and unreliable to varying degrees. They could generate false positives and/or false negatives to varying degrees.

Also, each of these tests comes with some risk. The screening tests are extremely low risk as to not bear mentioning for most people. But the diagnostic ones come with risks such as risk of miscarriage. If I recall, CVS testing carries a 1/100 risk of miscarriage, whereas amniocentesis carries a 1/200 risk.

Much more could be said depending on numerous other factors (e.g. maternal age).

Roe v. L'Chaim

There's a push to do the first trimester tests, before 20-24 weeks, because 24 weeks is the upper limit for when it's legally permitted to abort a child (depending on the state). After this point, one has to deal with all sorts of other legal issues and other complexities. For example, I think the coroner is supposed to get involved to check out the abortion if it's done after 20-24 weeks (depending on the state). In any case, some doctors sometimes put some pressure on some women to consider abortion prior to 20-24 weeks.

On the other hand, neonatologists have been able to rescue some 21-24 week old babies. Normal gestational period for humans is 38-42 weeks.