Relation of placenta to gestation period

The gestation periods of mammals vary widely. Animal size accounts for some of the differences, but research has now shown that the structure of the placenta is of paramount importance in determining gestation time.
The placenta plays an important role in the development of the young animal by providing the foetus with nutrients and oxygen and removing waste. The structure of the placenta, however, varies widely among species. According to the study, the structure determines the length of gestation. Placentas from 109 mammals were compared. The more complex and convoluted the placenta, the shorter the gestation. A complex placenta may be able to convey more nutrients to the developing young. This kind of complex placenta is seen in mice (gestation three weeks), dogs (two months) and leopards (three months). Humans and other primates have a much less complicated placenta, leading to slower growth and longer gestation.

In humans, the placenta has finger-like branches with relatively few connections between the tissues of mother and foetus. A leopard placenta forms a complex web of connections. This larger surface area enables much more exchange between the different tissues.

The form of the placenta is certainly not the only factor to determine gestation, researchers emphasize. The size of the animal and the developmental stage of the young are also important. Antelope young, for example, must be able to run with the herd immediately after birth, while many animal species are born into nests and cared for by their mothers for an extended period.