A retrospective evaluation of second-trimester serum screening for fetal trisomy 18: Experience of two laboratories

A retrospective study on screening methods for fetal trisomy 18 has been ca rried out in two different laboratories using the serum parameters: total h uman chorionic gonadotropin (hCG), unconjugated oestriol (uE3), and a-fetop rotein (AFP) in different combinations and in single marker protocols. Labo ratory A (L-A) utilized a radio-immunoassay to examine 38 fetal trisomy 18 cases and laboratory B (L-B) utilized an enzyme-immunoassay to examine 33 t risomy 18 cases. As unaffected references the whole routine cohorts of each laboratory were used (L-A: 29 043; L-B: 4264). In both trisomy 18 study gr oups the median hCG and uE3 multiples of the median (MoM) values were marke dly declined (L-A: 0.21 MoM, 0.37 MoM; L-B: 0.31 MoM, 0.44 MoM). Even after exclusion of trisomy 18 cases with combined neural tube or ventral wall de fects the medians of AFP MoM values were only moderately declined (L-A: 0.7 3 MoM; L-B: 0.8 MoM). Receiver-operator characteristic (ROC) curves after m ultivariate discriminance analysis and single marker evaluation demonstrate d that the difference of efficiency between a combination of hCG, uE3 and A FP, and a combination of hCG and uE3 is small but that any of these combina tions are more efficient than a combination of hCG and AFP or single marker protocols, respectively. At a risk cut-off generating a false-positive rat e of one per cent the most effective marker combination detected 31 of 38 ( 81.6 per cent) affected pregnancies in L-A and 25 of 33 (75.8 per cent) in L-B. The differences in sensitivity and specificity seem to be due to the d ifferent analytical systems being utilized by the two laboratories. Copyrig ht (C) 1999 John Wiley & Sons, Ltd.