Performance of conventional cytogenetic analysis on chorionic villi when only one cell layer, cytotrophoblast or mesenchyme alone, is analyzed.

From the perspective of identifying all abnormalities of potential clinical significance, the analysis of both placental layers is optimal. LTC alone is the preferred approach if only one layer of placenta is to be analyzed. Although rare, it is important to acknowledge that one cell layer analysis alone can cause misdiagnosis due to undetected mosaicism.