While it is well-understood what a normal human placenta should look like, a deviation from the norm can take many possible shapes. In this paper we propose a mechanism for this variability based on the change in the structure of the vascular tree.
@article{arxiv.0711.0796,
title = {Modeling the variability of shapes of a human placenta},
author = {Michael Yampolsky and Carolyn M. Salafia and Oleksandr Shlakhter and Danielle Haas and Barbara Eucker and John Thorp},
journal= {arXiv preprint arXiv:0711.0796},
year = {2008}
}