Wanting to know the sex of your baby can be as simple as knowing what colour to paint the nursery. However, it can also be vital to your child’s future health – there are certain disorders such as the neurological disease Duchenne muscular dystrophy or the bleeding disorder haemophilia that are linked with the sex chromosome, and while girls may be healthy carriers, boys carrying the gene are likely to develop the disease. There are also disorders such as congenital adrenal hyperplasia, where treatment before birth can prevent female foetuses becoming ‘masculinised’. South Korean researchers have used the polymerase chain reaction (PCR) to help them develop a diagnostic based on the ratio of the DNA expressing two enzymes in the mother’s blood. This could be developed into a simple blood test that identifies the sex of the developing foetus as soon as the first trimester (first three months of pregnancy), earlier than the procedures currently in use.

Pregnant woman

Existing tests for the baby’s sex are invasive, involving a sample of the amniotic fluid or the chorionic villus (part of the placenta). These carry a small (1-2%) risk of miscarriage and can’t be carried out until week 11 of pregnancy. Ultrasound scans can identify sex in later pregnancy but not until the second or third trimester, and the sex isn’t always clear, depending on how the baby is lying in the womb. Cell-free foetal DNA from the foetus enters the mother’s bloodstream from the placenta and makes up 3-5% of the total cell-free DNA in the blood. It is seen as early as week five, and clears shortly after the baby is born.

The team of researchers used a quantitative methylation-specific polymerase chain reaction of U-PDE9A to confirm that there was foetal DNA circulating in the blood, and then multiplex real-time polymerase chain reaction to quantify the levels of DNA coding for two enzymes, DYS14 and GAPDH. The results were compared with the sexes of the babies at birth and the team found that the ratio of the DNA for the two enzymes in the mother’s blood indicated whether the baby was a boy or a girl. The results are published in the FASEB Journal.

“Although more work must be done before such a test is widely available, this paper does show it is possible to predict the sex of a child as early as the first few weeks after conception,” said Gerald Weissmann, M.D., Editor-in-Chief of The FASEB Journal. “At present, parents are sometimes given the wrong information about the sex of their unborn child; this test should prove helpful in resolving any uncertainties of today’s ultrasound observations.”

Suzanne Elvidge is a freelance science, biopharma, business and health writer with more than 20 years of experience. She is editor of Genome Engineering, a blog that monitors the latest developments in genome engineering and that aims to educate (and sometimes to entertain!) and has written for a range of online and print publications including FierceBiomarkers, FierceDrugDelivery, European Life Science, the Journal of Life Sciences (now the Burrill Report), In Vivo, Life Science Leader, Nature Biotechnology, PR Week and Start-Up.