VIABLE PREGNANCIES AFTER DIAGNOSIS OF TRISOMY-16 BY CVS - LETHAL ANEUPLOIDY COMPARTMENTALIZED TO THE TROPHOBLAST

Increasing utilization of chorionic villus sampling (CVS) has lead to the discovery that the placenta can karyotypically be a very heterogen ous organ, and chromosomal mosaicism within the placenta can confuse c ytogenetic interpretation. Recently, confined placental mosaicism (con fined regions of aneuploidy in the otherwise normal diploid placenta a nd fetus) has been described involving a number of chromosomal abnorma lities. Fetal trisomy 16 is considered uniformly lethal early in gesta tion. However, we present 3 cases of nonmosaic trisomy 16 confined reg ionally to the placenta. We discuss the possible etiology, impact on t he developing fetus, and suggest an approach to the workup and evaluat ion of cases where the karyotype obtained on CVS is not compatible wit h the findings on ultrasound.