Relationship between gestational age and frequency of fetal trophoblasts and nucleated erythrocytes in maternal peripheral blood

The relationship between gestational age and frequency of fetal cells in th e maternal blood was studied in order to determine the optimal time for cel l recovery. The immunomagnetic colloid system was used to enrich nucleated erythrocytes (NRBCs) and trophoblasts from 20 mi maternal blood samples obt ained between 9 and 35 weeks' gestation (n = 41). Nested polymerase chain r eaction (PCR) for the Y chromosome of enriched NRBCs and trophoblasts showe d decreasing negative predictive values with increasing gestational age. Th e sensitivity and the overall frequency for correct fetal gender diagnosis were the lowest in the third trimester. Fluorescence in situ hybridisation (FISH) using XY DNA-specific probes was used to determine the fetal gender of the trophoblast-enriched fraction. The fetal origin of enriched NRBCs wa s determined using simultaneous immunophenotyping for fetal hemoglobin and FISH with XY probes. The mean number and mean percentage purity for both fe tal trophoblasts and NRBCs showed decreasing values with increasing gestati onal age. However, statistical analysis showed no relationship between gest ational age and frequency of fetal cells even though more fetal cells tend to exist during the first trimester. Nevertheless, the first trimester appe ars to offer the most optimal time fur fetal cell recovery from maternal bl ood for the purpose of prenatal diagnosis. Copyright (C) 2001 John Wiley & Sons, Ltd.