'Placenta key to pregnancy length' discovery ends 100-year mystery
Washington, Nov 17: A new research has revealed that the structure of the placenta has an important role in determining the pregnancy length in humans.
The research, which ends a 100-year mystery, links growth rates of mammals inside the womb to the structure of the placenta and the way it connects mother and baby.
The study, by Durham and Reading universities, shed light on how babies grow twice as fast in the wombs of some mammals compared to others.
It has found that the more intimate the connection is between the tissues of the mother and the foetus, the faster the growth of the baby and the shorter the pregnancy.
The findings also help to explain why humans, whose placentas do not form the complex web-like structure seen in animals such as dogs and leopards, have relatively lengthy pregnancies.
The structure of the placenta, however, varies enormously from species to species. This new study suggests these variations may play a role in the length of the pregnancy.
The researchers, who analysed 109 mammal species, studied the length of pregnancy, structure of placenta, and size of offspring in mammals, and examined how these characteristics have changed during the evolution of mammals.
They found that, despite the placenta essentially having the same function in all mammals, there were some striking structural differences.
They found that the more complex and folded the placenta of a mammal, the shorter the pregnancy time appeared to be.
The researchers also discovered that more folded placentas were able to deliver more nutrients to the infant.
"This study shows that it is not necessarily the contact with maternal blood which determines speed of growth, but the extent to which the tissues of mother and baby are 'interlocked', or folded, with one another," said lead author Dr Isabella Capellini.
"In humans, the placenta has simple finger-like branches with a relatively limited connection between the mother's tissues and those of the foetus, whereas in leopards, for example, it forms a complex web of interconnections that create a larger surface area for the exchange of nutrients," she added.
"Because we found no differences in the size of the babies when they are born, it seems that the outcome of this conflict is a kind of equilibrium in which faster growth is offset by a shorter pregnancy, " said co-author Professor Robert Barton from Durham University.
The findings are published in the academic journal American Naturalist.
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