Blood Test Can Tell Baby's Gender at 7 Weeks

Here’s a great news! A new blood test can determine a baby’s gender, with 95 percent accuracy, seven weeks into a pregnancy—without the risks of such invasive procedures as chorionic villus sampling or amniocentesis, both of which pose a small threat of triggering a miscarriage, reports an analysis to be published in the Journal of the American Medical Association on August 10. The blood test is already used in Europe and may be offered in the US as soon as 2012.

Currently, most expectant parents have to wait at least 11 to 12 weeks into the pregnancy, when an ultrasound may be able to detect a baby’s gender. However, first trimester results are wrong in up to 50 percent of cases: Earlier this year, Victoria Beckham was crushed when a scan seemed to indicate she was carrying a boy, only to be ecstatic when a subsequent ultrasound showed that she was actually expecting a girl.

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The new test provides valuable medical information to parents who have a family history of gender-linked diseases and could allow doctors to treat babies for some inherited disorders before birth, says study co-author Diana Bianchi, MD, executive director of the Mother Infant Research Institute at Tufts Medial Center.  However, the test also raises troubling ethical concerns, since it could also be used for gender selection, giving expectant moms the option of terminating a pregnancy earlier than ever before if the baby is the “wrong” gender. Here’s a closer look at the research.

How does the gender test work?  A sample of the pregnant woman’s blood is sent to a lab for cell-free fetal DNA testing. If the sample contains Y chromosomes, the baby is male, while absence of Y chromosomes indicates a girl. There are several ways to perform cell-free DNA testing. The study found that the best method uses a technique called real-time quantitative polymerase chain reaction.

How reliable are the results? The JAMA analysis, which pooled the results of 57 earlier studies involving 3,525 pregnancies in which the mom was carrying a boy, and 3,017 pregnancies in which the baby was a girl, found that the test results were 95 percent accurate at seven weeks, and nearly 100 percent accurate by 20 weeks.

What about online tests that claim to be able to tell a baby’s gender with 99.9 percent accuracy at 5 weeks? Don’t waste your money on these products. Such claims were what inspired the study, says Dr. Bianchi. “There is absolutely no scientific evidence that it’s possible to determine fetal gender with 99.9 percent accuracy at five weeks. Our analysis found that at that point in pregnancy, blood tests are 75 percent accurate at identifying male fetuses.”

What inherited disorders make it important to know a fetus’ gender? X-linked disorders, which include hemophilia and Duchenne muscular dystrophy, are carried on the X chromosome and strike males. Congenital adrenal hyperplasia, or CAH, is an inherited disorder that can cause a female fetus to develop “ambiguous genitals,” or even sex organs that look like those of a male. If the condition is detected in utero, says Dr. Bianchi, the mother can be treated with steroids, so that a baby girl with CAH isn’t born with masculine-looking genitals. CAH affects one in 14,000 babies, and has no adverse effect on the development of the genitals of a male infant.

Can expectant moms in the US get this test? Currently, no American academic or certified labs offer the test, according to Dr. Bianchi. There are online tests, but their reliability is questionable. However, some US ob/gyns and geneticists, including Dr. Bianchi, order the test through European labs if an expectant mom has a family history of gender-linked inherited disorders. Having the test can help such parents avoid the need for invasive procedures like amniocentesis, which can lead to a miscarriage in about one in 200 cases.

When will the test come to the US? Dr. Bianchi predicts that it may be available as early as next year. Since the blood test isn’t used to diagnose a medical condition, it doesn’t need FDA-approval, she adds. “With several companies soon to roll out a blood test for Down syndrome, there’s every reason to expect that the blood test to determine fetal gender will also be available next year, since it’s simpler to perform than the Down syndrome test.” The gender test could also help reduce medical costs, by decreasing the need for amniocentesis and chorionic villus sampling.