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The number of children born with Down's syndrome in Denmark halved over the past three years after non-invasive screening in early pregnancy was extended to women of all ages, new research reported at the conference of the European Society of Human Genetics shows.
The study assessed the effect of guidelines introduced by the National Board of Health in Denmark in 2004, which offer screening for Down's syndrome to all pregnant women rather than restricting it mainly to women aged over 35 years. Women were offered screening in the first trimester, measuring nuchal translucency in the fetus combined with a maternal blood test for chromosomal abnormalities.
Testing allowed a combined risk for Down's syndrome and other trisomies to be calculated. Women for whom the risk was more than one in 300 were offered an invasive procedure, analysing chromosomes from fetal cells obtained either by chorionic villus sampling or amniocentesis.
Data from the Central Cytogenetic Registry for three counties of Denmark with a total population of 1.1 million, equivalent to about one fifth of the national population, from 2004 to 2006 showed a doubling in the number of fetuses prenatally diagnosed as having trisomy 21 after introduction of the guidelines. This resulted in almost 50% fewer children born with Down's syndrome. The number of invasive procedures also decreased, from about 11% of all pregnancies to 5%.
Reporting the findings, Karen Brøndum-Nielsen, from the Kennedy Institute, Glostrup, Denmark, said, “Although we have not yet studied the whole of the population, these numbers are significant enough to show that the new guidelines have been accepted by a great majority of Danish parents.” It is important to investigate the psychosocial aspects of testing, however, she said.
Looking further into the history of children born with Down's syndrome showed that their mothers had often declined the offer of screening or had taken it too late in pregnancy. Other women had risk assessment that did not lead to invasive procedures.
See European Human Genetics Conference 2007, abstract C29, www.eshg.org/eshg2007.