Test looks for pieces of foetal DNA

Many genetic disorders affect only boys or girls - and so knowing a foetus's sex renders further tests unnecessary in around 50% of cases.

The UK's Institute of Child Health successfully trialled the test on more than 70 pregnant women.

Details will be presented at a British Society of Human Genetics meeting.

It avoids the risks associated with invasive testing in about half of the women Dr Lyn Chitty

The researchers tested women at risk of having babies affected by X chromosome-linked disorders that usually only affect boys, such as Duchenne muscular dystrophy.

They also tested women at risk of carrying girls with a condition called congenital adrenal hyperplasia (CAH), which causes the genitalia to develop abnormally.

If identified early enough, CAH can be treated in the womb using steroids.

In both cases, the new test revealed the gender of the foetus, weeks before it can be detected by ultrasound.

Team leader Dr Lyn Chitty said: 'The advantages of this test are clear when used in women at high risk of a genetic disorder.

"It allows for earlier determination of foetal sex than was previously possible using either chorionic villus sampling or ultrasound.

"It avoids the risks associated with invasive testing in about half of the women, and in some cases at risk of CAH patients could avoid taking steroids at all when the foetus was found to be male by seven weeks of pregnancy."

Miscarriage risk

Currently, to carry out a prenatal genetic test, scientists must obtain cells from the foetus, using either amniocentesis or chorionic villus sampling (CVS).

Both techniques involve injecting a needle into the womb, which can cause a miscarriage in up to 1% of cases. They also cannot be carried out until at least 11 weeks into the pregnancy.

Because of this, researchers have been trying for some time to develop a non-invasive technique for carrying out genetic tests during pregnancy.

In the latest study, the scientists worked on tiny amounts of 'free foetal DNA' found in the watery part of the mother's blood.

I can foresee ethical problems if the test were to be made widely available Professor Henry Halliday

At the moment the technique is limited to identification of genes which are only present in the father and can be passed on to the foetus.

This includes the sex determining genes or the rhesus gene when the father is rhesus positive and the mother rhesus negative.

Research is ongoing to find ways of improving the extraction of free foetal DNA so that more conditions can be diagnosed, such as cystic fibrosis or thalassaemia.

Professor Henry Halliday, an obstetrician at Belfast's Royal Maternity Hospital, said the test could certainly be useful.

However, he said: "I can foresee ethical problems if the test were to be made widely available - in some countries such as India and China there are significant imbalances in birth frequencies of boys and girls - probably due to selective termination of pregnancies with a female foetus.

"Clearly an accurate diagnosis of gender at seven weeks would greatly facilitate early abortion and this modifies one's enthusiasm for this new test."

Professor Nicholas Fisk, of Imperial College London, said similar work had already been reported by a French team.

But he said the latest study could lead to the test becoming more widely available.

Sex selection for 'family balancing' is not popular

The government intends to change the law to outlaw sex selection for non-medical reasons, she said.

Using the method for "family balancing" could be a "slippery slope in terms of people deciding that one gender is more important than the other", she said.

But Lib Dem Evan Harris says it is wrong for the state to restrict the reproductive choice of adults.

'Yuk' factor

Ms Flint made her comments during evidence to the science and technology committee, which is investigating IVF and embryo screening.

She told the MPs that there was some understanding about the use of sex selection of embryos where there was a serious medical condition, but it should not be for "family balancing".

The state should be giving good reasons before restricting the reproductive choice of adult citizens Dr Evan Harris

"We will be looking to see how we can make that clear in law so there is a very strong steer to the regulator about how that can be applied," she said.

But Dr Harris, a member of the science and technology committee, said: "Other than the public's 'yuk' reaction, the government gives no reason why parents of three boys shouldn't use pre-implantation sex selection to balance their family.

"Allowing such a move in no way suggests that one gender is better than another and so has no bearing on the negative attitudes to girls in some other countries.

"The state should be giving good reasons before restricting the reproductive choice of adult citizens."

Outdated law

The Department of Health has been conducting a review of the 1990 Human Fertilisation and Embryology Act - the legislation governing human fertilisation.

Advances in medical technology has rendered the act out of date and the government is anxious to update it.

As part of the review, a consultation exercise was carried out, which suggested that the public did not want the sex selection of babies for "social reasons" such as "family balancing".

The Human Fertilisation and Embryology Authority, which regulates this area for the government, has been waiting for a new draft bill containing this provision.

The science and technology committee has also been looking at MPs' calls for an end to the right of fertility clinics to refuse treatment to single women and lesbians.

Currently, clinics must take account of the welfare of the unborn child, including "the need for a father".

Opponents demanded a change in the law, saying the rule discriminates against single women and same-sex couples.

Ms Flint says issues around the "need for a father" were complex and the government was consulting on the issue.