Many expecting parents are eager to find out as soon as possible whether they’re having a boy or a girl. For a woman carrying a fetus that may be facing the risk of certain gender-linked disorders though, that information becomes so much more valuable.
Invasive tests like chorionic villus sampling and amniocentesis in rare cases carry the risk of miscarriage. An ultrasound may be able to accurately determine the baby’s sex as early as 13 weeks into the pregnancy, but clear results are not always possible.
Scientists funded by the National Human Genome Research Institute set out to investigate a method which is currently being used in some countries, though it isn’t licensed for clinical use in the U.S. The researchers tested the mom’s blood for bits of DNA from the fetus and if the results show DNA sequences from a Y chromosome, that indicates the fetus is male.
Researchers looked into previously published data from academic and hospital labs and found that the blood tests covered in the studies are quite accurate. The tests correctly identified a boy in 95.4% of the cases and a girl 98.6% of the time. As it turns out, accuracy depended on how long a woman was pregnant, because tests performed before seven weeks gestation weren’t reliable.
Some American companies sell gender-detection blood tests directly to consumers, but the technology they employ isn’t always identified, explains study co-author Diana Bianchi, a reproductive geneticist and executive director of the Mother Infant Research Institute at Tufts Medical Center. And there’s scarce published data on the accuracy of DTC tests. So these results can’t be used to support their use, she says.
The review also found that urine tests weren’t reliable at all.
Bianchi added that there are several different types of sex-linked medical conditions for which early identification of gender is important. For example, moms carrying a female fetus with a chance of developing a condition known as congenital adrenal hyperplasia must be treated with steroids throughout the pregnancy. By establishing the fetus is a boy, the mom can skip the treatment.