RESUMEN
OBJECTIVE: The aim of our study was to make a practical comparative evaluation of the first and second trimesters in order to determine the period during which a higher yield of fetal nucleated red blood cells (FNRBCs) can be obtained. METHODS: NRBCs were isolated from maternal blood during the first and second trimesters of pregnancy using double Percoll gradients with different osmolarities. Magnetic activated cell sorting was performed with Kleihauer-Betke stain. We isolated fetal NRBCs from 10 mL of samples of maternal blood and determined fetal sex and fetal aneuploidy by fluorescence in situ hybridization (FISH). RESULTS: The average number of NRBCs was 9.85 in samples obtained during the first trimester and 14.88 in samples obtained during the second trimester (P=0.07). The average number of NRBCs with Y chromosome signals was 5.73 in the first trimester and 8.22 in second trimester (P=0.56). However, the percentage of NRBCs with Y chromosome signals in the first trimester (70.6%) was significantly higher than in the second trimester (59.8%) (P=0.049). We diagnosed the blood samples from 7 pregnant women having fetal aneuploidy using this method and the number of NRBCs was 18.4. CONCLUSION: The method using Percoll osmolarity and a double density gradient system may be a very useful method for separation of NRBCs in the first trimester of pregnancy and also in the second trimester.