Progress in non-invasive pregnancy tests

Non-invasive prenatal tests to identifyfetuses at risk of genetic disorders as early as the sixth week of pregnancy are now a reality, say British scientists. A team based at the Institute of Child Health in London and Bristol has successfully carried out simple blood tests on more than 70 pregnant women, avoiding the need for further invasive tests in half of them. Team leader Dr Lyn Chitty presented the results at the annual meeting of the British Society of Human Genetics (BSHG), held at the University of York from 18-20th September.

The team tested women at risk of having babies affected by X-linked disorders that usually only affect boys, such as the blood clotting condition haemophilia. They also used the technique to test pregnancies at risk of a condition called congenital adrenal hyperplasia (CAH), which causes the genitalia of female fetuses to develop abnormally. If identified early enough, CAH can be treated in the womb using steroids. In both cases, the new test reveals the gender of the fetus, weeks before it is can be detected by ultrasound.

Dr 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 fetal sex than was previously possible using either CVS (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 fetus was found to be male by 7 weeks of pregnancy'.

Currently, to carry out a prenatal genetic test, scientists must obtain cells from the fetus, using either amniocentesis or CVS. Both techniques involve injecting a needle into the womb, which can cause a miscarriage in up to one per cent of cases. 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 fetal DNA' found in the mother's blood.

Also speaking about non-invasive prenatal tests at the BSHG meeting was Professor Diana Bianchi, of Tufts University School of Medicine in Boston. She told delegates that such tests could one day be used to gather detailed health information about the developing fetus, and could also be used to predict the risk of pregnancy complications. But she also warned that this new technology is being misused, in unreliable commercial tests that claim to detect a baby's gender as early as the second week of pregnancy.

A test based on the technique that claims to accurately predict gender using samples of the mother's blood as early as five weeks after conception has already been marketed. However, it is currently the focus of an ongoing lawsuit in the US, brought by women who say it got the gender of their babies wrong. Now, another company is claiming that it can determine fetal gender as early as one day after a missed period, using a sample of the mother's urine.

Professor Bianchi said: 'In some cases in the US some women have gone on to have unnecessary invasive prenatal diagnostic testing performed because their ultrasound results disagreed with the home fetal gender tests. This is not simply a matter of painting the nursery the wrong color. The unnecessary invasive tests carry a risk of miscarriage'.