From a total of 1312 diagnostic chorionic villus samplings (CVS) there were 22 which showed discordance between the karyotype of the chorionic villi and that of the fetus. This frequency was some 20-fold higher than that reported at amniocentesis. In the majority of discordant cases, the fetal karyotype was normal while the placental karyotype was mosaic. In four cases, the placental karyotype was non-mosaic (a trisomy 16, a monosomy X, and two tetraploids) while the fetal karyotype was normal. In one case, the placenta was trisomy 18 while the fetus was mosaic. There were two 'false-negative' results where short-term methods showed only normal cells while both long-term cultures of chorionic villi and fetal cells were mosaic, in one 46,XY/47,XXY and in the other 46,XY/47,XY,+21.

Karyotypic analysis of concepti spontaneously aborted in the first trimester shows approximately 50% of these concepti contain abnormal chromosomes. In order to determine whether cytomegalovirus (CMV) infection may play a role in the early loss of pregnancies with either normal or abnormal chromosomes, we have developed an assay to amplify CMV DNA in DNA extracts from spontaneously aborted concepti using the polymerase chain reaction (PCR). Using PCR, we were unable to detect CMV DNA in any of 350 spontaneously aborted concepti. Viral cultures were also negative when 36 of these were tested. Our results suggest that CMV infection is an unlikely cause of pregnancy loss in the first trimester of pregnancy.