Confined placental mosaicism

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Confined placental mosaicism (CPM) represents a discrepancy between the chromosomal makeup of the cells in the placenta and the cells in the baby. CPM was first described by Kalousek and Dill in 1983.[1] CPM is diagnosed when some trisomic cells are detected on chorionic villus sampling and only normal cells are found on a subsequent prenatal test, such as amniocentesis or fetal blood sampling. In theory, CPM is when the trisomic cells are found only in the placenta. CPM is detected in approximately 1-2% of ongoing pregnancies that are studied by chorionic villus sampling (CVS) at 10 to 12 weeks of pregnancy. Chorionic villus sampling is a prenatal procedure which involves a placental biopsy. Most commonly when CPM is found it represents a trisomic cell line in the placenta and a normal diploid chromosome complement in the baby.[2] However, the fetus is involved in about 10% of cases.[3]


CPM occurs in one of two ways:

Several factors influence the pattern of normal and abnormal cells in the developing embryo. Reduced or improved replication rates of the trisomic cells could affect the number of abnormal cells compared to the number of normal cells. The abnormal cells may fail to differentiate or function properly and could be lost. It is also possible that there is no selection against the abnormal cells, but their presence could compromise the pregnancy on a whole.[4]

Types of CPM[edit]

There are three types of confined placental mosaicism depending on the cells involved at the time of the error:

What does CPM mean for a pregnancy?[edit]

Most pregnancies that are diagnosed with confined placental mosaicism continue to term with no complications and the children develop normally.

However, some pregnancies with CPM experience prenatal or perinatal complications. The pregnancy loss rate in pregnancies with confined placental mosaicism, diagnosed by chorionic villus sampling, is higher than among pregnancies without placental mosaicism. It may be that sometimes the presence of significant numbers of abnormal cells in the placenta interferes with proper placental function. An impaired placenta cannot support the pregnancy and this may lead to the loss of a chromosomally normal baby.[5] 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 retardation (IUGR) has been reported in a number of CPM cases. In follow-up studies adequate postnatal catch-up growth has been demonstrated, which may suggest a placental cause of the IUGR.[6]

When predicting the likely effects (if any) of CPM detected in the first trimester, several potentially interactive factors may be playing a role, including:


  1. ^ Kalousek DK, Dill FJ (August 1983). "Chromosomal mosaicism confined to the placenta in human conceptions". Science 221 (4611): 665–7. doi:10.1126/science.6867735. PMID 6867735. 
  2. ^ a b c Robinson WP, Barrett IJ, Bernard L, et al. (April 1997). "Meiotic origin of trisomy in confined placental mosaicism is correlated with presence of fetal uniparental disomy, high levels of trisomy in trophoblast, and increased risk of fetal intrauterine growth restriction". American Journal of Human Genetics 60 (4): 917–27. PMC 1712477. PMID 9106539. 
  3. ^ a b c d e Phillips OP, Tharapel AT, Lerner JL, Park VM, Wachtel SS, Shulman LP (March 1996). "Risk of fetal mosaicism when placental mosaicism is diagnosed by chorionic villus sampling". American Journal of Obstetrics and Gynecology 174 (3): 850–5. doi:10.1016/S0002-9378(96)70312-5. PMID 8633655. 
  4. ^ Wolstenholme, J. (1996). "Confined placental mosaicism for trisomies 2, 3, 7, 8, 9, 16, and 22: Their incidence, likely origins, and mechanisms for cell lineage compartmentalization". Prenatal Diagnosis 16 (6): 511–524. doi:10.1002/(SICI)1097-0223(199606)16:6<511::AID-PD904>3.0.CO;2-8. PMID 8809892. 
  5. ^ Tyson RW, Kalousek DK (1992). "Chromosomal abnormalities in stillbirth and neonatal death". In Dimmick JE and Kalousek DK. Developmental pathology of the embryo and fetus. Philadelphia: Lippincott. pp. 103–109. ISBN 978-0-397-51040-5. OCLC 23868557. 
  6. ^ Fryburg JS, Dimaio MS, Yang-Feng TL, Mahoney MJ (June 1993). "Follow-up of pregnancies complicated by placental mosaicism diagnosed by chorionic villus sampling". Prenatal Diagnosis 13 (6): 481–94. doi:10.1002/pd.1970130610. PMID 8372074. 
  7. ^ a b Wolstenholme J, Rooney DE, Davison EV (May 1994). "Confined placental mosaicism, IUGR, and adverse pregnancy outcome: a controlled retrospective U.K. collaborative survey". Prenatal Diagnosis 14 (5): 345–61. doi:10.1002/pd.1970140505. PMID 8084856. 
  8. ^ Benn, Peter A.; Lillian Y. F. Hsu. "Prenatal Diagnosis of Chromosomal Abnormalities through Amniocentesis". In Aubrey Milunsky. Genetic Disorders and the Fetus: Diagnosis, Prevention and Treatment. Baltimore: Johns Hopkins University Press. pp. 214–296. ISBN 978-0-8018-7928-9. OCLC 52887000. 
  9. ^ Farra C, Giudicelli B, Pellissier MC, Philip N, Piquet C (March 2000). "Fetoplacental chromosomal discrepancy". Prenatal Diagnosis 20 (3): 190–3. doi:10.1002/(SICI)1097-0223(200003)20:3<190::AID-PD777>3.0.CO;2-A. PMID 10719319. 
  10. ^ Goldberg JD, Wohlferd MM (June 1997). "Incidence and outcome of chromosomal mosaicism found at the time of chorionic villus sampling". American Journal of Obstetrics and Gynecology 176 (6): 1349–52; discussion 1352–3. doi:10.1016/S0002-9378(97)70356-9. PMID 9215195. 

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