A test has been developed to determine the sex of an embryo from only five weeks old.

In the UK current tests can determine sex from 11 weeks after conception and as they are invasive, risk causing miscarriage. The new test, which was developed by scientists at the Kwan Dong University School of Medicine, Seoul, South Korea, relies on a blood sample from the mother and therefore carries no risk to the child.

The first trial, published in the FASEB Journal, used blood samples from 203 mothers between five and 12 weeks pregnant to verify the accuracy of the technique. By using the ratio of two enzymes in the women's blood – DYS14, the product of a gene found on the male-only Y chromosome, and GAPDH, found in both males and females – researchers were able to predict gender with 100 percent accuracy. In total, 99 boys and 104 girls were born.

The researchers say that the test may be useful to women who carry X-linked chromosomal abnormalities, such as the gene for haemophilia, and whose sons are therefore at high risk of having the disease. Dr Hyun Mee Ryu, the lead author, said that she thought the test 'can reduce the need for invasive procedures in pregnant women carrying an X-linked chromosomal abnormality and clarify inconclusive reading by ultrasound'.

The researchers also address the concern that their technique 'might promote the potential for sex selection. Therefore, there should be careful consideration about the use of this analytical tool in clinical situations'.

Indeed, news of the test sparked commentary from those concerned that the technique may be exploited for sex-selective terminations. In an editorial in the Canadian Medical Association Journal, interim editor Dr Rajendra Kale argues that the sex-selective terminations represent 'discrimination against women in its most extreme form'. He says that 'the solution is to postpone the disclosure of medically irrelevant information to women until after about 30 weeks of pregnancy'.

In the United States, a bill was proposed last year to outlaw abortions on the grounds of sex or racial selection. Healthcare professionals who perform or accept funding for such procedures would be prosecuted should the Act be passed by Congress.

Such laws are already in place in countries including India and South Korea where there is concern that the practice has led to an imbalance in the male-to-female ratio of live births. Critics of the proposal, however, argue that these laws are difficult to enforce and have had little impact on the gender ratio of babies born in the countries where they are in place. They also fear that such laws would reduce the availability and access of safe, legal terminations and other family planning services to women of ethnic minorities whose motives would be under greater scrutiny. Critics contend that clinics may even cease services to populations they feel are 'at risk' of such practices.

CLARIFICATION: The UK has UK Genetic Testing Network approval for non-invasive sex determination from seven weeks. This is available to women at high risk of sex-linked genetic diseases.