Toronto: Have you experienced childbirth complications and delivered a premature baby even after taking all de-stressing measures during pregnancy?

This could well be owing to stress in your mothers, grandmothers and beyond, suggests a study.

Inherited epigenetic effects of stress could affect pregnancies for generations.

"We show that stress across generations becomes powerful enough to shorten pregnancy length in rats and induce hallmark features of human preterm birth," said Gerlinde Metz from University of Lethbridge in Canada.

"A surprising finding was that mild to moderate stress during pregnancy had a compounding effect across generations. Thus, the effects of stress grew larger with each generation," Metz added.

For the study, the researchers examined the length of pregnancies in rats because in general there is very little variation between them.

A first generation of rats were subjected to stress late in pregnancy. The following two generations were then split into two groups that were either stressed or not stressed.

The daughters of stressed rats had shorter pregnancies than the daughters of those who had not been.

Remarkably, the grand-daughters of stressed rats had shorter pregnancies, even if their mothers had not been stressed.

The researchers believe that these changes are due to epigenetics - the arrangement and expression of our genes.

The study appeared in the journal BMC Medicine.

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