What cell type is most problematic if found in a CVS (chorionic villus) sample?

The presence of decidua in a chorionic villus sampling (CVS) is particularly problematic because decidua refers to the maternal tissue associated with the placenta. The primary goal of CVS is to obtain fetal tissue for genetic analysis, particularly chorionic villi, which are derived from the developing placenta and contain fetal genetic material.

When decidual tissue is present instead, it can complicate the analysis because it does not represent the fetus. The inclusion of maternal tissue may lead to inaccurate interpretations and results in genetic testing, as maternal genetic material can obscure or confound findings pertaining to fetal conditions. This can also hamper the ability to obtain a proper diagnosis or understanding of the fetus's genetic health.

In contrast, trophoblasts are normal components of the placenta and are expected in CVS samples, while fetal fibroblasts and amniotic cells are also representative of fetal tissue. Therefore, the identification of decidual tissue indicates that a sample may not be adequately representative of the fetal condition, making it a significant concern in the context of CVS.