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Confined placental mosaicism
1Department of Pathology, University of British Columbia, Yancouver, Canada.
Journal of Medical Genetics
|July 1, 1996
Summary
Confined placental mosaicism (CPM) occurs when a chromosomal abnormality is found only in the placenta, not the fetus. This condition affects approximately 2% of pregnancies and requires further testing for accurate diagnosis.
Area of Science:
- Prenatal Diagnostics
- Genetics
- Reproductive Medicine
Background:
- In most pregnancies, fetal and placental chromosomal complements are identical, originating from the same zygote.
- Confined placental mosaicism (CPM) is a condition where cytogenetic abnormalities are confined to the placenta.
- CPM was initially described in placentas of infants with unexplained intrauterine growth restriction (IUGR).
Purpose of the Study:
- To define and describe the phenomenon of confined placental mosaicism (CPM).
- To differentiate CPM from generalized mosaicism.
- To outline the diagnostic approach for CPM.
Main Methods:
- Cytogenetic analysis of chorionic villus sampling (CVS) at 9-11 weeks of gestation.
- Comparative analysis of placental (CVS) and subsequent fetal testing (amniotic fluid or fetal blood cultures).
- Karyotyping to detect chromosomal abnormalities like trisomy.
Main Results:
- Approximately 2% of viable pregnancies exhibit CPM.
- CPM involves tissue-specific chromosomal mosaicism affecting only the placenta.
- Diagnosis is confirmed when CVS shows mosaicism, but follow-up fetal testing reveals a normal diploid karyotype.
Conclusions:
- CPM is a distinct form of mosaicism, localized to the placenta.
- Accurate diagnosis of CPM relies on discordant results between placental and fetal testing.
- Understanding CPM is crucial for managing pregnancies with potential chromosomal abnormalities.