title: Distribution of fetal erythroblasts enriched from maternal blood in multifetal pregnancies.
abstract: BACKGROUND
  The aim of this study was to establish the frequency of fetal cells in the maternal blood of multifetal pregnancies and compare this figure with singleton pregnancies.
  
  
  METHODS
  We obtained maternal blood from 31 pregnancies with 2-6 fetuses at 11-16 weeks gestation and from 50 normal singleton controls (11-14 weeks gestation). Fetal erythroblasts were isolated from maternal blood using triple density gradient separation and anti-CD71 magnetic cell-sorting techniques. The enriched erythroblasts were stained with Kleihauer-Giemsa and with fluorescent antibodies for the zeta (zeta), epsilon (epsilon) and gamma (gamma) globin chains. The percentage of fetal cells positive for each stain was calculated. Fluorescence in-situ hybridization (FISH) for X and Y chromosomes was also performed.
  
  
  RESULTS
  The percentage of erythroblasts enriched from maternal blood that stained positive for zeta, epsilon and gamma globin chains and with Kleihauer-Giemsa was significantly higher in the multifetal compared with singleton pregnancies. The median enriched percentage of positively stained erythroblasts was about three times higher in the twin than in singleton pregnancies (P < 0.0001), nearly twice as high in the triplet than in twin pregnancies (P < 0.01) and five times higher in the triplet than singleton pregnancies (P < 0.0001). FISH for Y chromosome confirmed the increase in fetal cell proportion in the multifetal pregnancies.
  
  
  CONCLUSIONS
  These findings suggest that there is an increase in the physiological feto-maternal cell trafficking in multifetal pregnancies compared with singleton pregnancies, which is likely to be due to the increased placental surface area and vasculature.
authors.affiliation: Harris Birthright Research Centre For Fetal Medicine, King's College London School of Medicine, Denmark Hill, London SE5 9RS, UK.
authors.forename: Raghad
authors.initials: R
authors.lastname: Al-Mufti
authors.forename: Henry
authors.initials: H
authors.lastname: Hambley
authors.forename: Farzin
authors.initials: F
authors.lastname: Farzaneh
authors.forename: Kypros H
authors.initials: KH
authors.lastname: Nicolaides
mesh_terms: D000328:Adult; D041322:Chromosomes, Human, Y; D004900:Erythroblasts / Q000737:chemistry / Q000166:cytology*; D005260:Female; D005312:Fetal Blood; D005914:Globins / Q000032:analysis; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D008297:Male; D011247:Pregnancy; D011272:Pregnancy, Multiple / Q000097:blood* / Q000235:genetics; D013194:Staining and Labeling; D014310:Triplets; D014427:Twins
chemical_list: D005914:Globins