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Boy or girl? Pregnant women can now find out the sex of their聽fetus with a simple finger-prick test.

Until recently, expectant 鈥媘others usually had to wait until a mid-pregnancy ultrasound to find out their future child鈥檚 sex.

But in the last few years, increasing numbers of people have been finding out from a first-trimester blood test 鈥� called the聽聽鈥� that also detects Down鈥檚 Syndrome.

The test works by analysing fragments of the fetus鈥檚 DNA that have leaked into the mother鈥檚 bloodstream. It involves collecting about 20 millilitres of blood from the mother鈥檚 arm with a needle and syringe.

狈辞飞,听聽at Sabin Laboratory, a medical diagnostics company in Brazil, has made the test even simpler. His team has shown that a single drop of blood from a pregnant woman鈥檚 fingertip is enough to determine her fetus鈥檚 sex.

In a study of 100 pregnant women, they found that fingertip blood could be used to predict fetal sex with 100 per cent accuracy from 8 weeks鈥� gestation onwards.

The procedure was simple: they wiped each woman鈥檚 fingertip with dilute bleach to get rid of any foreign DNA that might contaminate the sample. A single drop of blood was collected by pricking her finger.

Each blood sample was then scanned for Y chromosome DNA. Only males carry the Y chromosome, so if it turned up in the mother鈥檚 blood, it must have come from her male fetus. If no Y chromosome was detected, the聽fetus had to be female.

Y do it?

The advantage of the finger-prick test is that it is faster, more convenient, and better for women who are scared of needles, says Barra. He believes women will have access to the test 鈥渧ery soon鈥�.

However, because it detects the fetus鈥檚 sex early in pregnancy, there is a risk it could lead to more sex-selective abortions, says聽聽at Royal North Shore Hospital in Sydney, Australia.

Sex-selective abortions are already known to happen in places like聽India听补苍诲听China, usually just after the mid-pregnancy ultrasound. Being able to test the fetus鈥檚 sex earlier could make this practice more common.

Generally, there鈥檚 no medical reason for checking the sex of a聽fetus in the womb 鈥� it鈥檚 mainly just for the parents鈥� interest, says McLennan. The exception is if a baby is at risk of having a serious genetic condition that depends on its sex, he says. For example, sons, but not daughters, can inherit Duchenne muscular dystrophy from their mother if she is a carrier.

Barra is now studying whether the finger-prick test can also be used to diagnose genetic conditions like Down鈥檚 syndrome in first trimester fetuses.