Fetal cells in maternal blood: a six-fold increase in women who have undergone amniocentesis and carry a fetus with Down syndrome: a multicenter study.

Fetal nucleated red blood cells (FNRBCs) circulate in the maternal blood throughout pregnancy. Even if the frequency of fetal cells in the maternal circulation remains to be ascertained, complications of pregnancy such as fetal cells aneuploidies, preeclampsia, abnormal Doppler of the uterine artery without symptoms of preeclampsia, fetal growth restriction and polyhydramnios are associated with an increased feto-maternal trafficking. Based on these observations, previous studies have suggested that determination of the fetal nucleated red blood cell count (FNRBCC) might be a useful non-invasive screening test, either alone or in combination with existing maternal tests, for the non-invasive assessment of aneuploidies, in particular Down syndrome (DS). In this paper we have evaluated the distribution of FNRBCC in a set of 18 normal pregnancies and 18 pregnancies with a trisomy 21-affected fetus, matching for gestational age, maternal age, and, when possible, fetal gender, in order to quantify the difference in the number of fetal cells between the two populations. Maternal blood was collected from each pregnant woman two to three weeks after amniocentesis after knowing the cytogenetic results. Correlation of FNRBCC with the gestational week and clinical status (affected vs. non affected) by multiple regression analysis provided significant results (p < 0.001). Adjusted values of FNRBCC were 48 +/- 10.2 in controls and 301 +/- 17.01 in DS cases, corresponding to a 6.27 fold increase. These retrospective results prompt a prospective evaluation of the use of FNRBCC for screening purposes.