A prospective two years study of first trimester screening for Down syndrome

Nowadays maternal age of pregnant women has increased in most developed countries. The rate of women above 35 years old constitutes about 15% of pregnancies.

The aim of our study is to prove that by first trimester screening, the number of women who have indication for invasive prenatal diagnostic procedure is significantly reduced.

This prospective study lasted two years from 02/2005 to 02/2007. The participants to our study were 531 pregnant women with a mean maternal age of 30 years (19-42). We used the first trimester screening test for Down's syndrome. The biochemical blood test of free b-hCG (beta human chorionic gonadotropin) and PAPP-A (pregnancy associated plasma protein A) and the measurement of nuchal translucency were performed between 11-13 weeks +6 days (mean gestational age 12 weeks +2 days).

In our study group, 69 women (12%) were 35 years old or more. The risk estimate for Down syndrome was 1 in 300 or more in 14 (2%) cases. In all these 14 cases we offered CVS (chorionic villus sampling) or amniocentesis.

It is a fact that although the risk of any individual 36 years old is higher, most abnormalities (approximately 70%) occur in the low risk population. With the first trimester screening the sensitivity of detecting DOWN syndrome reaches 90%. Our study confirms that by first trimester screening, the number of women who have indication for invasive prenatal diagnostic procedure is significantly reduced. As a result the cost for prenatal diagnosis of the population and also the risk of iatrogenic missed miscarriages is also reduced. Finally, this screening method gives the advantage of early diagnosis.