About 2 per cent of specimens from chorionic villus sampling (CVS) analysed either on direct preparation of cytotrophoblast cells or after culture of mesenchymal stroma reveal confined placental mosaicism (CPM), most commonly involving chromosomal trisomy. A significantly higher rate of prenatal loss (22 per cent) as well as the presence of intrauterine growth retardation (IUGR) has been reported among pregnancies with CPM. To evaluate more precisely the effect of these aneuploid cell lines confined to the placenta on intrauterine fetal growth and fetal survival, we have studied 34 term placentae from pregnancies with CPM diagnosed on CVS and confirmed identical mosaicism in 17 of these placentae. There was a direct correlation between a high number of aneuploid cells present at CVS and a high likelihood of their detection in term placenta. Also, the proportion of aneuploid cells in the mosaic term placentae correlated with that observed in CVS specimens. Among 17 gestations with confirmed CPM at delivery, there were six cases of IUGR identified, five in liveborns and one associated with intrauterine death.

III.

Confined chorionic mosaicism, detected commonly on chorionic villus sampling (CVS) and occasionally in cultured amniotic fluid cells, is described in five pregnancies that showed confined chorionic mosaicism for trisomies 12, 13, 14, 17 and a marker chromosome. Cytogenetic findings in these pregnancies support the conclusion that within chorion some chromosomal mosaicism are confined to the trophectoderm derivatives while others to the extra-embryonic mesoderm. The etiology of confined chorionic mosaicism is discussed in relation to a significant role of multiple cell lineages contributing to the early development of placenta. The need is indicated for the use of both direct and long-term cultures in CVS prenatal diagnosis, and for the confirmatory testing of fetal blood or amniotic fluid in cases where mosaicism is detected in chorionic villi.

The association of maternal uniparental disomy for chromosome 7 and postnatal growth failure has been reported in four cases and suggests the presence ofgenomic imprinting of one or more growth related genes on chromosome 7. However, in the reported cases, the possibility of homozygosity for a recessive mutation could not be excluded as the cause of the growth failure as in all cases isodisomy rather than heterodisomy for chromosome 7 was present. We report a case of prenatal and postnatal growth retardation associated with a prenatal diagnosis ofmosaicism for trisomy 7 confined to the placenta. DNA typing of polymorphic markers on chromosome 7 has established that the zygote originated as a trisomy 7 with two maternal and one paternal chromosomes 7 with subsequent loss of the paternal chromosome resulting in a disomic child with maternal heterodisomy for chromosome 7. The growth failure seen in this child with heterodisomy 7 lends strong support to the hypothesis of imprinted gene(s) on chromosome 7.