Cystyl aminopeptidase in maternal serum for the antenatal recognition of fetal growth retardation.

An appraisal has been made of the usefulness of cystyl aminopeptidase (CAS, E.C. 3.4.11.3) activity patterns in the in utero detection of fetal growth retardation; 196 pregnancies at risk from placental insufficiency, classified into 9 aetiologic groups were considered. Absolute levels and trend of enzyme activity were studied in all cases and compared with the reference range of CAS activity established in 267 healthy pregnant subjects. Excluding multiple pregnancies, overall predictive value of CAS in defining fetal outcome in 186 'at risk' pregnancies was 72%, overall sensitivity and specificity being 82% and 71% respectively; 48% of the 'at risk' population delivered growth retarded infants, whereas the prevalence of growth retardation as diagnosed by CAS was 54%. Out of the 89 patients who delivered growth retarded infants, 73 exhibited abnormal CAS activity patterns. In twin pregnancies, values of CAS in 73% of the total number of assays were above mean plus 2 standard deviations for the respective gestational period. CAS in maternal serum is advocated as a simple and reliable antepartum indicator of fetal growth retardation and is suitable for the detection of twin pregnancy as early as the second trimester.