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Shots - Health Blog
Tue August 9, 2011
Test a Mother's Blood To Learn Her Baby's Sex Early On
Boy or girl? Expectant parents are often dying to know. Some mothers are even trying to influence it with their diet. But the tests used to determine a baby's sex before birth leave a lot to be desired.
Blood tests that look for fetal DNA in a mother's blood would be a big improvement, according to a new study. But those tests aren't yet licensed for use in the United States, even though they're available in Europe. So parents who want an early peek into their baby's sex are stuck with dubious tests sold on the Web.
Consider the story of Baby Gender Mentor, a blood test for prenatal sex testing sold online in 2005. The company, Acu-Gen Biolab, marketed the test as "99.9 percent accurate" in detecting a fetus's sex as early as 5 weeks in.
But then, as NPR's Nell Greenfieldboyce reported, angry mothers started calling Acu-Gen, saying the baby they delivered – though adorable – was not the sex predicted. Needless to say, Baby Gender Mentor isn't available anymore.
As a result of the Baby Gender Mentor kerfuffle, Diana Bianchi, a professor of reproductive genetics at Tufts Medical Center in Boston, decided to try to find out if looking for fetal DNA in a mother's blood could be a more reliable early gender test.
She figured some parents might be interested in alternatives to ultrasound and the other, invasive tests that are typically used. Ultrasounds are not at all accurate before 12 weeks' gestation, and amniocentesis and chorionic villi sampling, which require removing small amounts of fluid and other cells from the womb, can cause miscarriage.
But Bianchi knew from research by herself and others that DNA from a fetus passes through the placenta into a mother's bloodstream, making it much more accessible. The easiest way to find baby DNA is by looking for the male Y chromosome, which women don't have.
Bianchi and her colleagues looked at studies of maternal blood to determine fetal sex, and found they were 75 percent accurate as soon as 7 weeks after conception. At 20 weeks, they were 99 percent accurate. The results were published today in the Journal of the American Medical Association.
But what about simple dipstick test, the kind that's used to test a woman's urine for pregnancy? The doctors also tested those tests sold online, and found them "worse than flipping a coin," Bianchi told Shots.
Bianchi says she sees real benefit in having maternal blood tests available for the couples she counsels, who often are facing very difficult issues with genetic disorders. For instance, only boys inherit hemophilia, so if a son could be identified early on, parents could move ahead with further testing. Doctors can't get the test done through labs in the U.S. because they haven't been approved by the Food and Drug Administration, but she says companies who sell the tests in Europe have been good about working with her and her patients.
Despite all the obvious benefits, the development of a simpler, faster test does raise bioethical questions. But Bianchi doesn't think that selling fetal DNA blood tests in the United States will increase the number of parents choosing to abort a child if it's not the sex they want. "Those same people can get an ultrasound now," she says.