Prenatal biochemical screening only detects half of chromosomal abnormalities

Women should be better informed before deciding to undertake it

Barcelona, Spain: Prenatal biochemical screening tests are widely used to look for chromosomal abnormalities in the fetus which can lead to serious handicap, or even death during gestation or in the first few days after birth. But these tests are only able to detect fewer than half of the total chromosomal abnormalities in the fetus, a scientist will tell the annual conference of the European Society of Human Genetics tomorrow (Monday 2 June) Dr. Francesca R. Grati, of the TOMA Laboratory, Busto Arsizio, Italy, says that these findings mean that women should be better informed on the limitations of such diagnostic tests.

The researchers studied 115,576 prenatal diagnoses carried out during the last fourteen years. 84,847 were amniocenteses, usually carried out around the 16th week of pregnancy, and 30,729 chorionic villus samplings, which can be undertaken from 12 weeks into the pregnancy. Both these tests carry an increased risk of miscarriage, so the decision on whether or not to undertake them can be difficult to weigh up. "Since our sample included a large number of women aged less than 35 who underwent invasive prenatal diagnosis without any pathological indication to do so, we felt that the results could be useful in helping to inform pre-test counselling of such women", says Dr. Grati. "Up until now, the information we had came from smaller studies which only looked at the performance of these tests in detecting a limited number of chromosomal abnormalities."

After analysing the results of the chromosomal abnormalities from their own dataset, the researchers combined them with the official detection rates for these abnormalities published by SURUSS and FASTER consortia. These are multi-centre research groups involved in the investigation of screening and diagnostic tests performed in pregnancy, whose results are being used to optimise prenatal care for pregnant patients. They found that current screening procedures were only able to detect half the total chromosomal abnormalities in women both younger and older than 35.