Quality control measures for placental sample purity in DNA methylation array analyses

The purity of tissue samples can affect the accuracy and utility of DNA methylation array analyses. This is particularly important for the placenta which is hypomethylated. Placental villous tissue from early pregnancy terminations can be difficult to separate from the non-villous tissue, resulting in potentially inaccurate results. We used several methods to identify mixed placental samples using DNA methylation array datasets from our laboratory and those contained in the NCBI GEO database, highlighting the importance of determining sample purity during quality control processes. Placental samples from 10 first trimester placentas (chorionic villi) were profiled using the Infinium HumanMethylation850 BeadChip.