Structural anomaly of the fetal membranes (also known as the amniochorionic or placental membranes), which comprise a vital intrauterine compartment, where they perform mechanical, immune, and endocrine functions to promote growth of the fetus and protection from environmental adversity. Amniochorionic membranes anatomically consist of a single layer of cuboidal amnion epithelial cells, chorionic trophoblasts, and scattered fibroblasts connected by a layer of type IV collagen-rich extracellular matrix. [from
HPO]