Pregnant women who endure the psychological stress of being in a war zone may be more likely to give birth to a child who develops schizophrenia, psychiatry researchers say.

Dr. Dolores Malaspina, a professor of psychiatry at the New York University School of Medicine and her colleagues analyzed medical records from more than 88,000 people who were born in Jerusalem from 1964 to 1976.

Females born to women who were in their second month of pregnancy during the Six-Day War between Arabs and Israelis in June 1967 were 4.3 times more likely to develop schizophrenia than females born at other times, the team reported in Wednesday's online issue of the journal BMC Psychiatry.

Males born to women at the same stage of pregnancy were 1.2 more likely to develop schizophrenia.

Role of stress hormones during pregnancy

"It's a very striking confirmation of something that has been suspected for quite some time," Malaspina said.

"The placenta is very sensitive to stress hormones in the mother. These hormones were probably amplified during the time of the war."

The stresses experienced during the war are those that would be experienced in a natural disaster such as an earthquake, terrorist attack or sudden bereavement, the researchers said.

"These findings add to a growing literature, in experimental animals and humans, attributing long-term consequences for offspring of maternal gestational stress," the study concluded. "They suggest both a sex-specificity and a relatively short gestational time-window for gestational effects on vulnerability to schizophrenia."

Last week, researchers in Montreal reported that babies born to women who were pregnant during the 1998 ice storm in Eastern Canada showed developmental delays such as lower IQ scores.

In that study, how mothers dealt with emotional stress was not judged significant, but objective exposure to stressors such as the number of days a woman went without power was deemed significant.

Pregnant women should not be alarmed about handling daily stressors since a developing fetus needs to be exposed to it, Malaspina said.

"But women experiencing anxiety or excessive stress would do well to address it before a planned pregnancy and to have good social support systems," she added.

While the study supports the hypothesis that vulnerability to schizophrenia increases during the second month of pregnancy, the link is not proven, the study's authors noted.