Boy or girl? A simple blood test in mothers-to-be can answer that question with surprising accuracy at about seven weeks, a research analysis has found.
Though not widely offered by U.S. doctors, gender-detecting blood tests have been sold online to consumers for the past few years. Their promises of early and accurate results prompted genetics researchers to take a closer look.
They analyzed 57 published studies of gender testing done in rigorous research or academic settings - though not necessarily the same methods or conditions used by direct-to-consumer firms.
The authors say the results suggest blood tests like those studied could be a breakthrough for women at risk of having babies with certain diseases, who could avoid invasive procedures if they learned their fetus was a gender not affected by those illnesses. But the study raises concerns about couples using such tests for gender selection and abortion.
Couples who buy tests from marketers should be questioned about how they plan to use the results, the study authors said.
The analyzed test can detect fetal DNA in mothers' blood. It's about 95 percent accurate at identifying gender when women are at least seven weeks' pregnant - more than one month before conventional methods. Accuracy of the testing increases as pregnancy advances, the researchers concluded.
Conventional procedures, typically done for medical reasons, can detect gender starting at about 10 weeks.
The new analysis, published in Wednesday's Journal of the American Medical Association, involved more than 6,000 pregnancies. The testing used a lab procedure called PCR that detects genetic material - in this case, the male Y chromosome. If present in the mother's blood, she's carrying a boy, but if absent, it's a girl.
Tests that companies sell directly to consumers were not examined in the analysis. Sex-detection tests using mothers' urine or blood before seven weeks of pregnancy were not accurate, the researchers said.
Senior author Dr. Diana Bianchi, a reproductive geneticist and executive director of the Mother Infant Research Institute at Tufts Medical Center in Boston, called the results impressive. She noted doctors in Great Britain are already using such testing for couples at risk of having children with hemophilia or other sex-linked diseases, partly to help guide treatment decisions.
The research indicates that many laboratories have had success with the test, but the results can't be generalized to all labs because testing conditions can vary substantially, said Dr. Joe Leigh Simpson, a genetics professor at Florida International University. He was not involved in the study.
Simpson noted that using gender-detection blood testing for medical or other reasons has not been endorsed by guideline-setting medical groups and some experts consider it experimental.
Dr. Lee Shulman, chief of clinical genetics at Northwestern Memorial Hospital in Chicago, said the testing "isn't ready for prime time."
He said his hospital doesn't provide the blood tests, and doesn't offer more conventional techniques, including amniocentesis, to women who have no medical reason for wanting to know their baby's gender.
"I would have a lot of difficulties offering such a test just for gender identification. Gender is not an abnormality," Shulman said. "My concern is this is ultimately going to be available in malls or shopping centers," similar to companies offering "cute" prenatal ultrasound images.