Levels of urinary beta-core fragment, total oestriol, and the ratio of the two in second-trimester screening for Down syndrome

Levels of beta‐core fragment and total oestriol in second‐trimester maternal urine samples were measured in 32 Down syndrome pregnancies and 206 control pregnancies. Beta‐core fragment and total oestriol values were corrected for the urinary creatinine level and expressed as multiples of the control medians (MOM). In addition, the ratio of the beta‐core fragment level to the total oestriol level, without creatinine correction, was calculated, and expressed as MOM values. The median beta‐core fragment, total oestriol, and ratio levels in Down syndrome cases were 5·42, 0·64, and 9·32 MOM, respectively. In the Down syndrome pregnancies, 66 per cent of the beta‐core fragment levels were above the 95th centile of control levels, while 22 per cent of the total oestriol levels were below the fifth centile of control levels. In combination with maternal age, measurement of beta‐core fragment and total oestriol levels in Down syndrome pregnancy resulted in an 80 per cent detection rate at a 5 per cent false‐positive rate. Use of the ratio resulted in a univariate detection rate of 72 per cent. In combination with maternal age, the ratio resulted in a detection rate of 81 per cent at a 5 per cent false‐positive rate. Based on this unmatched study, the measurement of a ratio of beta‐core fragment to total oestriol levels, without the need for creatinine correction, may be useful in screening for fetal Down syndrome in second‐trimester urine. © 1997 John Wiley & Sons, Ltd.