Pregnant moms can transmit stress through placenta

Mother to baby

A pregnant mother may pass on damaging experience of stress to her unborn baby through the placenta, a new study has found.

Researchers from the University of Pennsylvania School of Veterinary Medicine found that if a mother is exposed to stress during pregnancy, her placenta translates that experience to her foetus by altering levels of a protein that affects the developing brains of male and female offspring differently.

The findings suggest one way in which maternal-stress exposure may be linked to neurodevelopmental diseases such as autism and schizophrenia, which affect males more frequently or more severely than females.

“Most everything experienced by a woman during a pregnancy has to interact with the placenta in order to transmit to the foetus,” said Tracy L Bale, senior author of the study published in the Proceedings of the National Academy of Sciences.
“Now we have a marker that appears to signal to the foetus that its mother has experienced stress,” Bale said.

The study builds on previous work by Bale and her colleagues which found that female mice exposed to stress during pregnancy gave birth to males who had heightened reactions to stress.

Further research showed that the effect extended to the second generation: The sons of those male mice also had abnormal stress reactions.

The Penn team hoped to find a biomarker that could account for these changes and risk factors. To be an effective signal of maternal stress, the researchers reasoned, a biomarker would need to show differences in expression between male and female offspring and would need to be different between stressed and unstressed mothers.
They also wanted to find a marker that behaved similarly in humans.

They went about their search by first exposing a group of female mice to mild stresses, such as fox odour or unfamiliar noises, during the first week of their pregnancies, a time period equivalent to the first trimester of a human pregnancy. Another group of pregnant mice was unexposed.

In a genome-wide screen of the female’s placentas, one gene stood out as meeting the researchers’ criteria: Ogt, an X-linked gene that codes for the enzyme O-linked-N-acetylglucosamine transferase (OGT).

Placentas from male offspring had lower levels of OGT than those from female offspring, and all placentas from stressed mothers had lower levels than placentas from their unstressed counterparts.

The study suggested that the OGT enzyme may be acting to protect the brain during gestation but that males have less of this protective enzyme to begin with, placing them at an increased risk of abnormal neurodevelopment if their mother is stressed during pregnancy.