CONFINED PLACENTAL CHIMERISM - PRENATAL AND POSTNATAL CYTOGENETIC ANDMOLECULAR ANALYSIS, AND PREGNANCY OUTCOME

The presence of two cell lines in chorionic villi sampling (CVS) repre sents a significant complication in CVS analysis, interpretation, and counseling. We report on the cytogenetic and molecular analysis of a p regnancy that was conceived on clomiphen citrate. Two cell lines (46,X X and 47,XY, + 9) were discovered in CVS analysis done for maternal ag e; 94% of the cells in the culture were 46,XX and 6% were 47,XY, + 9 ( the direct preparation was 46,XX). As neither line could have derived from the other, chimerism and not mosaicism was suspected, with the 47 ,XY, + 9 cells deriving from a co-twin whose demise was the result of the autosomal trisomy. At a subsequent amniocentesis, only normal fema le cells were observed and a normal female infant was delivered at ter m. Cytogenetic analysis done on the infant's peripheral blood and on a sample of an umbilical vessel showed only 46,XX cells, while amnion a nd a fibrotic area of the placenta contained 2 cell lines, 46,XX and 4 7,XY, + 9. Molecular analysis of 3 different tissues was done by the p olymerase chain reaction (PCR) and Southern blotting, using Y specific primers and probes, respectively. The presence of Y specific DNA was detected in the placenta and amnion, but not in the umbilical blood ve ssel. These data excluded true chimerism in the fetal tissues at the l evel of about 1 in 10(5) cells and have defined for the first time pro bable confined placental chimerism (CPC), the result most likely of a ''vanishing twin.'' Whenever two cell lines are found in CVS, especial ly in the setting of pharmacologically stimulated ovulation, the possi bility of CPC should be considered. The effects of CPC on placental fu nction and fetal outcome merit further study. (C) 1994 Wiley-Liss, Inc .