Prenatal screening misses defects

Tests conducted during pregnancy do not pick up all genetic defects in the foetus, Italian research shows. The study, conducted on over 100,000 prenatal diagnoses which used invasive tests such as amniocentesis, found that the tests identified only half of chromosomal abnormalities. Speaking at the annual conference of the European Society of Human Genetics, Dr Francesca Grati, of the TOMA Laboratory in Italy, said: "Our research confirms that it is fundamental for doctors to counsel patients about the limitations of current screening methods, so that they can make an informed decision on whether or not to undergo invasive diagnostic testing."

Amniocentesis, in which a needle is used to take a sample of the fluid in the womb, is not routinely offered to women in the UK as it is invasive and can increase the risk of miscarriage.

The test can help identify chromosomal abnormalities including those which cause Down's Syndrome, Edward's Syndrome and Patau Syndrome.

But Dr Grati said that these are "common" and that "there are many others which are not picked up by these tests".

Down's Syndrome is one of the best known examples of chromosomal abnormalities. It occurs when babies have an extra copy of one of the chromosomes and leads to problems in cognitive and physical development, cardiac defects and a characteristic facial appearance.