Test can determine fetal sex at 7 weeks

According to a recent study in The Journal of the American Medical Association (JAMA),1 a simple blood test can determine a baby's sex as early as seven weeks into pregnancy is highly accurate if used correctly. Experts say this blood test is likely to lead to more widespread use by parents concerned about gender-linked diseases, those who are merely curious, and people considering the more ethically controversial step of selecting the sex of their children.

The test, which analyzes fetal DNA found in the pregnant woman's blood, can determine the sex of the fetus weeks earlier than other options, such as ultrasound, and is noninvasive, unlike amniocentesis and other procedures that carry small risks of miscarriage.

The tests have been available to consumers in drugstore chains and online for a few years, but their use has been limited, partly because their accuracy was unclear. One company, which guaranteed 99.9% accuracy as early as five weeks into pregnancy, filed for bankruptcy after a lawsuit by scores of women whose tests showed the opposite sex of the baby they ended up having.

European doctors routinely use the tests to help expectant parents whose offspring are at risk for rare gender-linked disorders to determine whether they need invasive and costly genetic testing. For example, Duchenne muscular dystrophy affects boys, but if the fetus is not the at-risk sex, such tests are unnecessary. But doctors in the United States generally have not prescribed the tests because they are unregulated and medical labs are not federally certified to use them.

That issue and other aspects of the pregnancy landscape could change as a result of the new study. The study analyzed large amounts of research on fetal DNA tests — 57 studies involving about 6,500 pregnancies — and found that carefully conducted tests could determine sex with accuracy of 95% at 7 weeks to 99% at 20 weeks.

One potential ethical issue is that women might abort fetuses of an undesired sex. Several companies do not sell tests in China or India, where boys are prized over girls and fetuses found to be female have been aborted. While sex selection is not considered a widespread objective in the United States, companies say that occasionally customers expressed that interest and have been denied the test. A recent study of third pregnancies in the journal Prenatal Diagnosis2 found that in some Asian-American groups, more boys than girls are born in ratios that are "strongly suggesting prenatal sex selection," the authors said.

At least one company, Consumer Genetics, which sells the Pink or Blue test, requires customers to sign a waiver saying they are not using the test for that purpose. "We don't want this technology to be used as a method of gender selection," said the company's executive vice president, Terry Carmichael. Sex-determination tests are part of a new frontier of fetal DNA testing, which can be used to determine paternity and blood type and is being used to develop early screening tests for genetic diseases such as Down syndrome.

The tests are not regulated by the Food and Drug Administration because they are not used for medical purposes, a spokeswoman said, but the agency is investigating the explosion of home genetic tests such as these and genome-sequencing kits. A typical blood test like Pink or Blue, for example, costs $25 for the kit. Lab fees and shipping costs, which vary, bring the total expense to $265 to $330.

References

  1. Devaney SA, Palomaki GE, Scott JA, et al. Noninvasive fetal sex determination using cell-free fetal DNA: A systematic review and meta-analysis. JAMA 2011; 306:627-636.
  2. Egan JFX, Campbell WA, Chapman A, et al. Distortions of sex ratios at birth in the United States; evidence for prenatal gender selection. Prenatal Diagnosis 2011; 31:560-565.