DIFFERENTIAL INCREASES IN AFP, HCG, AND UE3 IN TWIN PREGNANCIES - IMPACT ON ATTEMPTS TO QUANTIFY DOWN-SYNDROME SCREENING CALCULATIONS

Since the advent of multiple marker screening (MMS) for Down syndrome (DS) risk calculations, limitations for twins have been apparent, Rece nt attempts have been made to extrapolate mathematically singleton ris ks to twins. Here we investigate the pattern of levels among AFP, hCG, and uE3 in twins, MMS screening data from 4,443 twin pregnancies were compared to those from 258,885 singletons from 14-21 weeks of gestati onal age during a 3-year period (1992-1994) in our laboratory, Medians were determined for singletons and twins, and the ratios of twins to singletons were derived, Median AFP levels for twins are approximately double those of singletons, but median increases for hCG and uE3 are less than double, The data were divided further by ethnic groups (whit e, African American, Asian, and Hispanic), among which there were sign ificant variations in medians, but not in the ratios of twins to singl etons, The increased serum levels of different markers in twins are no t consistent across analytes, possibly reflecting independent developm ent of different compartments, Such differences mean that a mere mathe matical conversion of singleton DS risks would be imbalanced among the analytes and cannot be applied reasonably to twins, Ethnic specific d atabases are as important in twins as they are in singletons. (C) 1997 Wiley-Liss, Inc.