Screening for trisomy 18 by fetal nuchal translucency and maternal serum free beta-hCG and PAPP-A at 10-14 weeks of gestation

In a study of 50 cases of trisomy 18 compared with 947 controls we have fou nd the median multiple of the median (MoM) of maternal serum free beta huma n chorionic gonadotrophin to be significantly decreased (0.281 MoM) in samp les collected between the 10th and 14th week of gestation. Similarly, mater nal serum pregnancy associated plasma protein A (PAPP-A) levels are also de creased (0.177 MoM), whilst the median nuchal translucency is significantly higher (3.272 MoM). Free beta-hCG MoM was less than the 5th centile of nor mal in 64 per cent of cases of trisomy 18 and for PAPP-A was less than the 5th centile in 78 per cent of cases. Also, in 78 per cent of cases the nuch al translucency was above the 95th centile. When combined together in a mul tivariate algorithm with maternal age, we predict that 89 per cent of cases of trisomy 18 could be detected at a 1 per cent false-positive rate. We co nclude that specific trisomy 18 risks should be part of developing risk alg orithms combining maternal serum biochemistry and nuchal translucency for u se in first trimester screening alongside those for trisomy 21. (C) 1999 Jo hn Wiley & Sons, Ltd.