Testing for fetal DNA in a pregnant woman's blood can accurately predict the child's sex, researchers have found.
In a review of previous research, such tests were able to accurately pin down sex at least 95 percent of the time, Stephanie Devaney of the National Institutes of Health in Bethesda, Md. and colleagues reported in the August 10 issue of the Journal of the American Medical Association.
Non-invasive DNA testing may provide an alternative to more invasive tests, such as chorionic villus sampling and amniocentesis -- which can carry a slight risk of pregnancy loss -- for determining the gender of a fetus and related heritable disorders, the researchers wrote.
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Those disorders include ambiguous genitalia, X-linked conditions, and single-gene disorders such as congenital adrenal hyperplasia.
The presence of cell-free circulating Y-chromosome DNA sequences in the blood of pregnant women was first described in 1997, and has been widely studied since then, albeit in studies that have been limited methodologically.
In some countries -- the Netherlands, U.K., France, and Spain -- cell-free fetal DNA testing has already become a part of routine clinical care despite the lack of large performance studies.
Gender can typically be accurately assessed via sonogram at 13 weeks, but diagnosis with ultrasound isn't always possible, the researchers explained, and earlier diagnosis is often favorable.
In order to look at overall performance of the blood tests, the researchers conducted a review and meta-analysis of 57 studies conducted between Jan. 1, 1997 and April 17, 2011, totaling 80 data sets on 3,524 male-bearing and 3,017 female-bearing pregnancies.
Generally, they found high sensitivity and specificity for Y-chromosome detection in maternal blood (95 percent and 99 percent, respectively).
They also found that performance was best when performed at 20 weeks' gestation or later.
Tests done using urine samples and those run prior to seven weeks' gestation were unreliable, the researchers said.
Devaney and colleagues noted that a disadvantage of fetal DNA blood testing is the need to validate female sex, because the test looks for male, or Y-chromosome, DNA. Also, the test is not currently available at the doctor's office, has not yet been approved by the Clinical Laboratory Improvement Amendments (CLIA), and is not currently reimbursed by insurers.
They also noted that many of the included studies were small, so it would be "beneficial to help validate test performance under highly controlled testing conditions."
This could also help test manufacturers to "ensure that their claims are accurate," as some companies that directly market the tests to consumers say their products have an accuracy of 95 percent to 99 percent as early as five to seven weeks' gestation.