It’s amazing to me that fetal DNA floats free in the mother’s blood

Scientists Confirm: Blood Test Can Tell A Fetus’s Sex at Seven Weeks
[Via 80beats]

What’s the News: A blood test can reliably tell a mother-to-be whether to expect a boy or girl as early as seven weeks into pregnancy, according to a new analysis published today in the Journal of the American Medical Association. The test can distinguish the sex of a fetus up to three months earlier than an ultrasound can, and doesn’t carry the slight risk of miscarriage that accompanies invasive tests such as amniocentesis.

How the Heck:

The test works by detecting tiny bits of fetal DNA floating through an expectant mom’s bloodstream. In particular, the test looks for little fragments of a Y chromosome, which only males have. Some Y chromosome DNA in the blood sample means it’s a boy; none means it’s a girl. Of course, this method isn’t perfect. The test could fail to recognize a minute amount of male DNA in a sample, or mistakenly detect a bit of a Y chromosome where there isn’t. So, the researchers set out to determine just how accurate this test was. They analyzed all the data from 57 previous studies of the technique, looking at a combined total of more …


The numbers look really good. About 10% of the DNA found floating free in a pregnant woman comes from the fetus. And this DNA has a turnover time in days, so it is unlikely to come from any other source. In fact, using the free floating DNA is more accurate than trying to use any fetal cells found in the blood.

Using Y chromosome specific sequences, the tests were able to identify male fetuses. If there was no male fetus DNA found, the fetus turned out to be female.

The sensitivity and specificity of these tests approach 99% accurate. in addition, it appears that chromosomal abnormalities and genetic defects will easily be able to be determined.

For couples with possible genetic factors underlying their pregnancy, these technologies could offer great hope.

2 thoughts on “It’s amazing to me that fetal DNA floats free in the mother’s blood

  1. In countries with a bias toward sons, wouldn’t they be self-correcting when there are no girls for the guys to marry?

Comments are closed.