BACKGROUND: Identification of fetal nucleated red blood cells (NRBCs) in 
maternal circulation can facilitate non-invasive prenatal diagnosis, but 
technical difficulties still exist. An increase in the number of circulating 
NRBCs, however, could indicate fetal aneuploidies or pregnancy complications.
MATERIALS AND METHODS: The number of NRBCs was determined from 20 mL peripheral 
blood in 351 women in the second trimester of pregnancy after isolation by 
magnetic cell sorting (MACS) with anti-CD71 antibody and identification with 
May-Grunwald/Giemsa staining.
RESULTS: An average of eight NRBCs (range 1-12) were identified among 282 women 
with chromosomally normal fetuses. In cases known to carry aneuploid fetuses the 
mean number was 35 (range 7-113), but when the fetus had trisomy 21 (n = 17) an 
average of 71 NRBCs were identified. Among 26 carriers of beta-thalassemia, 42 
NRBCs (range 22-158) were isolated. In pregnancies with abnormal Doppler 
findings in both uterine arteries (n = 20), 15 NRBCs (range 2-75) were isolated.
CONCLUSION: Determining the number of NRBCs in maternal circulation could 
represent an additional screening step for fetal aneuploidies, as long as the 
anemic status of the mother is taken into consideration. However, more cases 
with abnormal Doppler results must be investigated before this test is used for 
in the prediction of pregnancy complications.