Review: A high capacity of the human placenta for genetic and epigenetic variation: Implications for assessing pregnancy outcome

Genetic and epigenetic studies of the human placenta can help to clarify the underlying mechanisms of placenta-associated diseases. However, such studies have also revealed a considerable degree of within- and between-placenta variability, which can be attributed to a variety of influences. We illustrate the inherent heterogeneity in the placenta using examples from two types of studies: 1) chromosomal mosaicism and 2) DNA methylation variation. We discuss the factors that may influence the distribution of variation and how, understanding the source of this variation is important for interpreting data used to investigate and predict clinical outcomes.