Girls born to stressed mothers are themselves more likely to give birth prematurely, scientists have found.
Canadian researchers believe that stress can alter the genes, meaning mothers-to-be can pass it on to their babies - affecting pregnancies for generations to come.
The University of Lethbridge study involved subjecting rats to stress late in pregnancy and observing their offspring.
The results, published in the journal BMC Medicine, found the daughters of stressed rats had shorter pregnancies than the daughters of those who had not been.
And remarkably, the grand-daughters of stressed rats had shorter pregnancies, even if their mothers had not been stressed.
Professor Gerlinde Metz said: "We show that stress across generations becomes powerful enough to shorten pregnancy length in rats and induce hallmark features of human preterm birth.
"A surprising finding was that mild to moderate stress during pregnancy had a compounding effect across generations."
Prof Metz believed these changes were due to epigenetics - the arrangement and expression of genes.
She added these changes are due to microRNA (miRNA) - non-coding RNA molecules that play a role in regulating gene expression.
She said: "Previous epigenetic studies have mainly focused on inheritance of DNA methylation signatures.
"What we didn't know was whether microRNAs, which are important biomarkers of human disease, can be generated by experiences and inherited across generations.
"We have now shown that maternal stress can generate miRNA modifications with effects across several generations."
Future research is planned to understand the mechanisms that generate these epigenetic signatures and how they are passed down from generation to generation.
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With more knowledge of these mechanisms it may be possible to predict and prevent preterm pregnancy but also other diseases.
Prof Metz added: "Preterm births can be caused by many factors, in our study we provide new insights into how stress in our mothers, grandmothers and beyond could influence our risk for pregnancy and childbirth complications.
"The findings have implications outside of pregnancy, in that they suggest that the causes of many complex diseases could be rooted in the experiences of our ancestors.
"When we better understand the mechanisms of inherited epigenetic signatures, we can predict disease risk and potentially reduce the future risk of illness."
- Daily Mail