The length and structure of placenta may play a key role in the gestation period in mammals and human beings.

Placenta, key to reproduction in mammals, helps passing on nutrients and oxygen from the parent to the fetus. Scientists have found out that the mammals with the most complex placenta structure has less gestation period compared to the ones with simpler placenta structure. These complex placenta structures help in the transfer of more nutrients and oxygen helping better fetus growth, thus reducing gestation period.

"In humans, the placenta has simple finger-like branches with a relatively limited connection between the mother's tissues and those of the fetus," said Dr Isabella Capellini of Durham University, the lead author on the study. "Whereas in leopards, the placenta forms a complex web of interconnections that create a larger surface area for the exchange of nutrients."

Mice, with the most complex placenta structure among the mammals, have the least pregnancy period, three weeks. Human beings and baboons with simpler placenta have the longest gestation time.

But, the researchers agree that the structure of placenta is not the only factor that decides gestation period in animals. There are other factors like the weight of the animal, the fetuses’ ability to grab more nutrients from the parent, the animals’ place in the food pyramid and its survival instinct. "From the moment of conception, the physiologies of mother and baby are adapted to achieve slightly different goals in terms of how fast the baby grows," said Professor Robert Barton, of Durham University.

The placenta plays a crucial role in mammal gestations as it facilitates to and fro movement of oxygen, nutrients and waste. The study, published in the journal American Naturalist have analyzed 109 mammal species to arrive at this conclusion. This finding will help the scientist to successfully explain the different gestation time in animals with similar weight.