Most pregnancies that are diagnosed with<unk>  continue to term with no complications and the children develop normally. However, some pregnancies with<unk>  experience prenatal or perinatal complications. The pregnancy loss rate in pregnancies with<unk> , diagnosed by chorionic villus sampling, is higher than among pregnancies without<unk>  mosaicism. It may be that sometimes the presence of significant numbers of abnormal cells in the<unk> interferes with proper<unk>  function. An impaired<unk> cannot support the pregnancy and this may lead to the loss of a chromosomally normal baby. On the other hand, an apparently normal diploid fetus may experience problems with growth or development due to the effects of uniparental disomy (UPD). Intrauterine growth restriction (IUGR) has been reported in a number of<unk>  cases. In follow-up studies adequate postnatal catch-up growth has been demonstrated, which may suggest a<unk>  cause of the IUGR. When predicting the likely effects (if any) of<unk>  detected in the first trimester, several potentially interactive factors may be playing a role, including: *Origin of error: Somatic errors are associated with lower levels of trisomy in the<unk> and are expected usually to involve only one cell line (i.e.: the trophoblast cells or the villus stroma cells). Somatic errors are thus less likely than meiotic errors to be associated with either ultrasound abnormalities, growth problems or detectable levels of trisomy in small samples of prenatal CVS. Currently, there is no evidence that somatic errors, which lead to<unk><unk>  trisomy, are of any clinical consequence. Errors of meiotic origin are correlated with higher levels of trisomy in<unk>  tissues and may be associated with adverse pregnancy outcome. The cell type in which the abnormality is seen is also an important factor in determining the risk of fetal involvement. The villus stroma or mesenchymal core is more likely than the cytotrophoblast to be reflective of the fetal genotype. *Level of mosaicism: There is a correlation between a high number of aneuploid cells detected at CVS with poor pregnancy progress. This includes an association between high levels of abnormal cells in<unk>  tissue and concerns with the growth of the baby. However, it is not accurate to use these associations to try to predict pregnancy outcome based on the percent of trisomic cells in a first trimester CVS result. *Specific chromosomes: The influence of<unk>  on fetal growth is chromosome specific. Certain chromosomes carry imprinted genes involved in growth or<unk>  function, which may contribute to impaired pregnancy progress when<unk>  is detected. Different chromosomes are observed at different frequencies depending on the type of<unk>  observed. The pregnancy outcome is strongly chromosome specific. The most frequently seen trisomic cells in<unk>  involve chromosomes 2, 3, 7, 8 and 16. The next frequently involved are 9, 13, 15, 18, 20 and 22. It has been observed that<unk>  involving the sex chromosomes usually has no adverse effects on fetal development. The common autosomal trisomies (21, 18, 13) made up a smaller number of cases of mosaicism detected on CVS, but were more often confirmed in fetal tissue (19%). On the other hand, the uncommon autosomal trisomies accounted for a greater number of<unk>  mosaicism cases, but were less often confirmed in fetal tissue (3.2%). When<unk>  is detected on CVS involving certain chromosomes which are known or suspected to carry imprinted genes, molecular investigations should be performed to exclude fetal UPD. We will explore chromosome specific cases in the chromosome specific section. *Type of chromosome abnormality: The factor that had the highest predictive value as to whether the fetus was affected or not was the type of chromosome abnormality. Marker chromosomes were more often confirmed in the fetus than trisomies. For example, of 28 cases of mosaic polyploidy detected on CVS, fetal mosaicism was confirmed in only one case. This is compared to marker chromosomes detected on CVS, in which mosaicism was confirmed in 1/4 of the fetuses.
Confined placental mosaicism
Germline mosaicism
Fetal programming
Robertsonian translocation
Uniparental disomy
Transplacental carcinogenesis
Postzygotic mutation
Paternal age effect