The largest study to be carried out on serum screening for Down's syndrome has shown that it can be performed accurately during the first trimester of pregnancy. This confirms previous findings suggesting that tests - currently carried out in the second trimester - should be carried out earlier.
The US study screened 4,412 pregnant women, mostly over the age of 35, for serum concentrations of a range of markers associated with Down's syndrome. Tests identified 61 foetuses with Down's syndrome, 48 of which were identified before 14 weeks of gestation. The detection rate was 63 per cent and 60 per cent respectively when tests for human chorionic gonadotrophin and its free beta subunit - standard testing for Down's syndrome - were each used in combination with the test for pregnancy associated protein A.
Researchers believe the findings provide further evidence that it is possible to carry out serum screening earlier.
But a report from the Health Technology Assessment programme, which did not include this latest study, concludes that there should be carefully monitored programmes before a decision is made to introduce widespread first-trimester screening.
Haddow J, Palomatri G, Knight G et al.
Screening of maternal serum for fetal Down's syndrome in the first trimester.
New England J of Medicine 1998; 338(14): 955-61; Wald N, Kennard A, McGuire A.
Antenatal Screening for Down's Syndrome. Health Technology Assessment 1998; 2(1).