Placentophagy: Clean the Nest Site?

Most animals consume their placenta after birth. Humans are in the minority in that we don't regularly practice placentophagy. In fact, if you were to ask most women if they were going to save their placenta after birth, they would look at you as if you had two heads. Many theories have been brought to light to try and explain why animals ingest their placenta after birth. The cleaning of the nest site theory is one that is often discussed as an explanation for placentophagy. It basically states that placentophagy protects the newborn and mother from being detected by predators.

However, the cleaning of the nest site theory for placentophagy does not account for the many other variables of labor and delivery. One being other fluids that are left behind following a birth. All of which would attract a predator and none of which are also cleaned up in any way. Furthermore, many animals that are actually predators themselves consume the placenta after birth. A perfect example is a lion. Lions have no predators hunting them in the wild. Yet a lioness will ingest her placenta after birth. She has no reason to clean the nest site to protect her young. She is perfectly capable of protecting her young all by herself, if needed. She must be practicing placentophagy for some other reason.

In looking at other species of animals, not all animals need to stay in the place that have given birth. Such animals would be able to evacuate the site because their young are immediately mobile. They could just get up and walk away. Yet these same animals stay, many for hours, consuming the placenta in it's entirety. If these animals were concerned about predators, they would quickly "clean up" and move on to another location.

In conclusion, for me personally as a midwifery student, the most interesting reason that the cleaning of the nest site is most likely only a tiny piece of the placentophagy puzzle is the evolutionary purpose behind ingestion of the placenta. For those mothers that are Rh negative, the ingestion of the placenta could help the mother’s immune system by suppressing the Rh antigen. When a mother is Rh negative and is carrying a baby that is Rh positive, the mother can develop antibodies to the Rh antigen. Those antibodies can attack the baby's red blood cells. This can cause severe life threatening problems with the baby. The ingestion of the placenta can prevent the mother from developing the antibodies that lead to these complications. This last reason for placentophagy, to me, is one of the most promising explanations available.