Women usually learn their baby's sex through an ultrasound, at 18 to 20 weeks.
Proponents of the blood test say this may be particularly valuable for families that harbor sex-linked genetic disorders like hemophilia. “It could reduce the number of invasive procedures that are being performed for specific genetic conditions,” said Dr. Diana Bianchi of Tufts University School of Medicine, who worked on the new study.
The technology works by detecting "cell-free fetal DNA," or DNA from the fetus, says author Diana Bianchi of the Tufts University School of Medicine in Boston.
Researchers analyzed 57 published studies of gender testing done in rigorous research that showed that these blood tests, common in Europe but not in the U.S., can reveal a fetus' sex only a week or two after a pregnant woman has missed her period.
The test is used in some European countries and “What they are finding in England is that many women are not going on to have the invasive tests,” Bianchi told Reuters Health.
After seven weeks into a pregnancy, tests that analyze mom’s blood for fetal DNA can correctly identify a male fetus 95.4 percent of the time and a female fetus 98.6 percent of the time on average, according to the study.
The Associated Press reports the test is 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.
Dr. Lee Shulman, chief of clinical genetics at Northwestern Memorial Hospital in Chicago, said the testing isn't quite ready to be fully implemented by physicians and hospitals.
"I would have a lot of difficulties offering such a test just for gender identification. Gender is not an abnormality," Shulman told AP. "My concern is this is ultimately going to be available in malls or shopping centers," similar to companies offering "cute" prenatal ultrasound images.
Shulman 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.