DNA testing via blood test may offer an early way to establish the sex of a fetus

THE QUESTION Might DNA tests on a pregnant woman’s blood or urine offer a simple, reliable way to determine her baby’s sex?

THIS STUDY analyzed data from 57 studies, involving 6,441 pregnancies, that included DNA testing of blood or urine samples at various times during pregnancy to establish the presence or absence of the Y chromosome, which indicates a male fetus. Blood testing was more accurate when it was conducted later in the pregnancy: 95 percent accurate at seven weeks, for example and 99 percent accurate at 20 weeks into a pregnancy. Results before seven weeks were deemed unreliable, as was all DNA testing on urine samples.

WHO MAY BE AFFECTED? Pregnant women and their fetuses. Amniocentesis is a more invasive way to establish the sex of a fetus and carries a small risk for miscarriage. Ultrasound, which is not invasive and is less risky, is generally not used before 11 weeks and may not produce reliable results till later. Besides easing the curiosity factor, establishing sex can be useful if a fetus is considered at risk for certain types of genetic diseases.

CAVEATS In DNA testing, absence of a Y chromosome in a blood sample does not always mean the fetus is female; it could mean that the sample contained no fetal DNA. The tests in the study are reportedly used routinely in Britain, France, Spain and other countries and are available via the Internet. The Food and Drug Administration does not regulate their use.

FIND THIS STUDY Aug. 10 issue of the Journal of the American Medical Association (

LEARN MORE ABOUT DNA testing at (click “Genetics & Medicine,” then “GeneTests”). Read about prenatal tests at (click on parents’ site).

Linda Searing

The research described in Quick Study comes from credible, peer-reviewed journals. Nonetheless, conclusive evidence about a treatment's effectiveness is rarely found in a single study. Anyone considering changing or beginning treatment of any kind should consult with a physician.