Urinary free beta hCG, beta core fragment and total oestriol as markers ofDown syndrome in the second trimester of pregnancy

In a study of 69 random urine samples from cases of Down syndrome and 405 s amples from unaffected pregnancies, we have assessed the value of various c andidate markers that have been proposed as tools for screening for Down sy ndrome. We found that the marker urine free beta hCG in Down syndrome had a median MoM of 3.53 (95 per cent confidence interval 2.48-4.68) and at a 5 per cent cut-off would have identified 49 per cent (34/69) of cases. Urine beta core had a median MoM of 4.95 (387-8.62) and at a 5 per cent cut-off w ould have identified 39 per cent (27/69) of cases. Total oestriol had a med ian MoM of 0.65 (0.55-0.80) and at a 5 per cent cut-off would have identifi ed 35 per cent (24/69) of cases. Tn conjunction with maternal age, the mode lled detection rate increased to 55.8 per cent for free beta hCG, 49.8 per cent for beta core and 48.8 per cent far total oestriol. In combination fre e beta hCG, total oestriol and maternal age would have detected 68 per cent of cases for a 5 per cent false-positive rate. Using analyte ratios to obv iate the need to correct for urine dilution in our study (rather than corre cting to a fixed creatinine concentration) was not shown to be as effective as correcting using urine creatinine. Urine markers on the whole are unlik ely to be of practical screening value considering the 85 per cent to 90 pe r cent detection rates achievable in the first trimester using a combinatio n of ultrasound and maternal serum biochemistry. Copyright (C) 1999 John Wi ley & Sons, Ltd.