Scientists Confirm: Blood Test Can Tell A Fetus's Sex at Seven Weeks

By Valerie Ross | August 10, 2011 5:07 pm

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 than 6,500 pregnancies.
  • At 7 to 12 weeks, the researchers found, the test determined the sex of a fetus with 95% accuracy. At 20 weeks, the test got it right 99% of the time.

What’s the Context:

Reference: Stephanie A. Devaney, Glenn E. Palomaki, Joan A. Scott, & Diana W. Bianchi. “Noninvasive Fetal Sex Determination Using Cell-Free Fetal DNA.” Journal of the American Medical Association, August 10, 2011. DOI: 10.1001/jama.2011.1114

Image courtesy of Fred Jala / Flickr

CATEGORIZED UNDER: Health & Medicine
  • Whoah

    Wait, a 7 week old fetus can have sex with another fetus? I want in on this!

  • anon

    Interesting article. Just a slight correction, that “gender” and “sex” are different concepts, and so while it may be possible to accurately determine a fetus’s “sex”, it’s less likely to determine the “gender.” In fact, I personally don’t quite think fetuses can be gendered.

  • IW

    You mean a blood test can tell a fetus’s gender at seven weeks, don’t you? Contrary to Whoah’s suggestive suggestion, fetuses don’t have sex at seven weeks. At least I sure don’t recall it…. And if ‘anon’ is referring to sexual orientation, then I’d agree that he or she (or it?!) is correct, too.

  • Cathy

    No, the article is correct. Gender is defined as an individual’s mental association with one sex or the other – e.g. masculine or feminine. The actual sex itself is male or female.

  • bicay

    I don’t know why we have to go so far off topic here. Gender is not defined only as an individual’s mental association. When the author writes about ‘gender’ in this article he is not referring to grammar, which is the first definition in most dictionaries. The author is not using the word to refer to the non-widely used cultural situation of sexual preference, which is the second or third definition in most dictionaries. He is talking about the biological sex of a human fetus, which is a valid definition of the word gender, and the only one that makes sense in this article. Can’t we just leave it at that? See the note on usage below:

    Usage Note: Traditionally, gender has been used primarily to refer to the grammatical categories of “masculine,” “feminine,” and “neuter,” but in recent years the word has become well established in its use to refer to sex-based categories, as in phrases such as gender gap and the politics of gender. This usage is supported by the practice of many anthropologists, who reserve sex for reference to biological categories, while using gender to refer to social or cultural categories. According to this rule, one would say The effectiveness of the medication appears to depend on the sex (not gender) of the patient, but In peasant societies, gender (not sex) roles are likely to be more clearly defined. This distinction is useful in principle, but it is by no means widely observed, and considerable variation in usage occurs at all levels.

    The American Heritage® Dictionary of the English Language, Fourth Edition copyright ©2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.

  • mopoco

    @anon: “In fact, I personally don’t quite think fetuses can be gendered.”

    What does that mean? Gender used as a verb means the same as engender = “1. To bring into existence; give rise to. 2. To procreate; propagate.”, in which case, fetuses not only can, but MUST be ‘gendered’.


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