SCREENING FOR DOWN-SYNDROME IN THE FIRST TRIMESTER

Second-trimester maternal serum screening for Down syndrome is now wel l established, and permits detection of up to 70% of cases. The disadv antage of this sort of screening is that the timing of maternal blood sampling is relatively late (after 15 weeks). There is an accumulating body of evidence to suggest that in the first trimester concentration s of a number of pregnancy-associated proteins and hormones differ in chromosomally normal and abnormal pregnancies. A first-trimester mater nal serum screening test for Down syndrome may therefore be possible. In addition, new methods of screening have recently been described bas ed on ultrasound findings at 11 to 13 weeks of gestation. This review article presents a discussion of published data on the feasibility of first-trimester screening for Down syndrome.