RÉSUMÉ
Detection of Circulating Fetal Trophoblastic Cells [CFTC] by single cell genotyping not only allows to identify fetal cells from maternal blood, but also to characterize their bi-parental genome. We have tested intact fetal trophoblastes recovered at 4th to 10th weeks of gestation [WG] from blood [10 ml per mother] of 13 women after In Vitro Fertilization [IVF] and transfer of one or several embryos. Large cells isolated from blood were individually microdissected and studied by genetic fingerprinting with a mean number of 3 Short Tandem Repeats [STR] markers, known to be informative by testing paternal and maternal blood DNA. CFTC were found in all mothers starting from the 5th WG. A mean number of 2.5 CFTC per ml of blood was found in all the analyzed samples collected at the different terms of pregnancy. All mothers who received the transfer of two or three embryos, including one who delivered twins and one with vanishing twin [identified by ultrasounds], were found to have CFTC with two or three different bi-parental genotypes, belonging to different embryos derived from the same parents. CFTC circulation is detectable starting from the 5th WG. A "vanishing twin" phenomenon frequently develops after IVF and transfer of multiple embryos, being undetectable by ultrasounds and revealed by genetic CFTC fingerprinting