Pregnant women who were traumatized by witnessing the Sept. 11 attacks on the World Trade Center may have passed on a biological sign of stress to their unborn babies, scientists said.

Researchers found the women and their babies had reduced levels of the stress hormone cortisol, which is a sign someone has been affected by post traumatic stress disorder.

Low levels of cortisone have been observed in the children of Holocaust survivors, but researchers had put them down to living with a depressed parent or hearing stories about what had happened to them.

The latest study suggests however that a mother can pass on low cortisol levels to her unborn child, researchers at the Mount Sinai School of Medicine in New York and the University of Edinburgh in Scotland said.

“This shows that exposure to severe stress in pregnancy is associated not only with PTSD in the mothers but also with the biologic marker of it -- low hormone levels in the saliva -- in the offspring long before they could have been listening to tales,” Professor Jonathan Seckl, of the University of Edinburgh, said in an interview.

Seckl said it was too early to tell if the children would suffer any ill effects. The researchers plan to follow up the children during their development. 

辅助阅读：因目睹9.11世贸中心恐怖袭击而受到精神伤害的怀孕妇女可能会将这种精神紧张的生物信息传递给未出生的婴儿。