P11.13: First trimester biochemical markers of Down syndrome and placental mosaicism

Le résumé fourni par la source

In our recent experience with 1750 patients who had 1st trimester screening of down syndrome, on the basis of maternal age, nuchal measurement and biochemical markers (free B HCG and PAPP-A) we have observed that there may be more discrepancies between fetal karyotypes obtained from chorionic villus sampling (CVS) and amniocentesis, than had been reported before. It is common in most laboratories to observe a difference of 1% to 2% between CVS and amniocentesis concerning placental-confined mosaicisms. As the levels of free B HCG and PAAP-A reflect the placental function, and are considered in the calculation of risk of Down syndrome, the question can be asked whether an increased risk can be due to placental mosaicisms or other abnormalities. Among 1750 patients, 101 had a CVS. The fetal karyotype was obtained by direct preparation (syncitiotrophoblast) and after cell cultures (cytotrophoblast). Among these 101 patients, in 8 cases it was impossible to assess the normality of the karyotype because some abnormalities were observed: trisomy 2 mosaicism in 2 cases; trisomy 7 mosaicism in 1 case; trisomy 15 mosaicism in 1 case; monosomy X mosaicism in 3 cases. An amniocentesis was performed in all 8 cases. Fetal karyotype obtained from amniotic cells was normal in 6 cases, except mosaicism of monosomy X in 2 cases. In case of trisomy 15, testing for uniparental disomy was also performed and the result was negative. The rate of placental-confined mosaicism in this short series was 6% (6/101). Among these 8 patients, in 7 cases the increased risk was due only to abnormal levels of biochemical markers. Knowledge of an increased risk of placental mosaicism without fetal chromosomal abnormality in cases of abnormal levels of biochemical markers may influence genetic counseling and the choice between CVS and amniocentesis assuming that such results could be confirmed on a larger scale.

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