Risk of fetal mosaicism when placental mosaicism is diagnosed by chorionic villus sampling, ,

OBJECTIVE: Our purpose was to determine the risk of fetal mosaicism when placental mosaicism is found on chorionic villus sampling. STUDY DESIGN: We present a case of mosaic trisomy 22 detected on chorionic villus sampling and subsequently found in the fetus. A review of comprehensive chorionic villus sampling studies with emphasis on follow-up for fetal mosaicism was conducted. RESULTS: Among 13 studies reviewed, 469 cases of placental mosaicism are presented; fetal mosaicism was found in 50 (10.7%). Factors associated with fetal mosaicism are (1) mosaicism on mesenchymal core culture and (2) type of chromosome abnormality involved - specifically, marker chromosomes (26.7%) and common autosomal trisomies (19.0%). Amniocentesis predicted fetal genotype in 93% to 100% of cases of placental mosaicism, depending on the cell type in which mosaicism was diagnosed. CONCLUSIONS: Although mosaicism is usually confined to the placenta, the fetus is involved in about 10% cases. Patients should be counseled about this risk and the accuracy of follow-up amniocentesis. (AM J OBSTET GYNECOL 1996;174:850-5.)