A placental diploid cell line is not essential for ongoing trisomy 13 or 18 pregnancies

Viable trisomy 13 or 18 pregnancies may be supported by the presence of a d iploid cell line, confined to the outer layer of the placenta (cytotrophobl ast). To establish the presence of diploid cells we investigated five rando m biopsies from placentas of trisomy 13 (n=8) and trisomy 18 cases (n=6) of newborn infants and terminated pregnancies by means of fluorescence in sit u hybridisation on interphase nuclei (n=100). In 12 of these 14 placentas ( including all five liveborns) 80% or more of the analysed nuclei showed thr ee spots, suggestive of the presence of a full trisomy. In the other two pl acentas (both cases of trisomy 18) mosaicism was detected at most investiga ted sites. Thus, in contrast with earlier studies, these results show that a significant diploid cell line present in the placenta, confined to the tr ophoblast, is not a pre-requisite for intrauterine survival in the investig ated cases.