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Extra embryonic/fetal karyotypic discordance during diagnostic chorionic villus sampling
D F Callen1, G Korban, G Dawson
1Cytogenetics Unit, Adelaide Children's Hospital, South Australia.
Prenatal Diagnosis
|July 1, 1988
Summary
Chorionic villus sampling (CVS) revealed chromosomal abnormalities in 22 cases, with placental mosaicism frequently leading to normal fetal karyotypes. This highlights potential discrepancies in genetic testing during pregnancy.
Area of Science:
- Prenatal diagnosis
- Cytogenetics
- Reproductive medicine
Background:
- Chorionic villus sampling (CVS) is a common prenatal diagnostic tool.
- Discordance between placental and fetal karyotypes can occur, necessitating careful interpretation.
- Amniocentesis has a lower reported rate of karyotypic discordance compared to CVS.
Purpose of the Study:
- To investigate the frequency and nature of karyotypic discordance between chorionic villi and fetal cells in diagnostic CVS.
- To compare the rate of discordance in CVS with that reported for amniocentesis.
Main Methods:
- Analysis of 1312 diagnostic chorionic villus samplings (CVS).
- Karyotyping of both chorionic villi (placenta) and fetal cells.
- Evaluation of discordant cases, including placental mosaicism and non-mosaic abnormalities.
- Assessment of 'false-negative' results using short-term and long-term culture methods.
Main Results:
- Twenty-two out of 1312 CVS cases (approximately 1.67%) showed karyotypic discordance between the placenta and fetus.
- The frequency of discordance in CVS was significantly higher (about 20-fold) than that reported for amniocentesis.
- In most discordant cases, the fetus had a normal karyotype while the placenta showed mosaicism.
- Four cases presented with a normal fetal karyotype and a non-mosaic abnormal placental karyotype (Trisomy 16, Monosomy X, two tetraploidies).
- One case showed a trisomy 18 placenta with a mosaic fetus.
- Two 'false-negative' results occurred where short-term CVS cultures were normal, but long-term cultures and fetal cells revealed mosaicism (46,XY/47,XXY and 46,XY/47,XY,+21).
Conclusions:
- Karyotypic discordance between the placenta and fetus is a notable finding in chorionic villus sampling.
- Placental mosaicism is the primary driver of discordance, often resulting in a normal fetal karyotype.
- The higher rate of discordance in CVS compared to amniocentesis warrants careful consideration in prenatal genetic testing strategies.
- Potential for 'false-negative' results emphasizes the importance of appropriate culture methods in CVS interpretation.