Blood drawn from expectant mothers could offer parents an earlier peek at their baby's sex than methods currently used in the US researchers said.
The test may be particularly valuable for families that harbour sex-linked genetic disorders like haemophilia, they added.
Because such disorders mostly strike boys, knowing that the baby is a girl could spare the mother from diagnostic procedures, such as amniocentesis, that carry a small risk of miscarriage.
"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.
Undesirable sex of a child could lead to termination
But other researchers voiced concerns, saying it could be misused to terminate a pregnancy if the baby isn't of the desired sex.
"What you have to consider is the ethics of this," said Dr Mary Rosser, an obstetrician and gynaecologist at the Montefiore Medical Centre in New York.
"If parents are using it to determine gender and then terminate the pregnancy based on that, that could be a problem," she told Reuters Health. "Remember, gender is not a disease."
The test looks for small pieces of the male sex chromosome in the mother's blood, which would mean she is carrying a baby boy. Some European hospitals already rely on the method, called cell-free foetal DNA, although it's not available in the US.
Boy children are more desirable than girls
"What they are finding in England is that many women are not going on to have the invasive tests," Dr Bianchi told Reuters Health.
In a fresh look at the medical evidence for the blood test, she and her colleagues analyzed 57 earlier studies that included more than 6,500 pregnancies.
They found parents could trust the test 98.8% of the time when it said they'd have a boy, and 94.8% of the time when it indicated a girl.
That leaves some room for error, which could be important if parents are making medical decisions based on the results – such as whether or not to have invasive procedure to look for genetic disorders.
Invasive alternative does not spot sex of the baby
However, the current non-invasive alternative – an ultrasound done at the end of the first trimester – isn't always good at spotting a baby's sex, Dr Bianchi's team note in their paper, published online in the Journal of the American Medical Association.
And the blood test is reliable as early as seven weeks into the pregnancy, whereas ultrasound is not.
Dr Bianchi said one study had estimated the blood test costs about 255kg in the UK. While it's available over the Internet, she said her team had only looked at hospital-based test performance.
"I don't know why it is not being incorporated in the US," she said.
Test raises ethical issues
Dr Rosser, however, chalked that up to the ethical issues it raises.
"It is a great test that can be part of our armamentarium of non-invasive testing that we use," she said. "But it should only be used by families that are at risk for sex-linked diseases."
Dr Bianchi owns stock in Verinata Health, a company that is developing cell-free foetal DNA tests for Down syndrome, although that company had no role in the new study.
The American College of Medical Genetics did not respond to requests for comment on the DNA tests.
(Reuters Health, August 2011)