WASHINGTON (Reuters) - Pregnant women who live through wars are more likely to give birth to a child who develops schizophrenia, U.S. researchers reported on Thursday in a study linking prenatal stress with the mental illness.

Afghan women clad in burqas walk along a road past destroyed houses in Kabul June 12, 2008. REUTERS/Ahmad Masood

Babies born to women who were in their second month of pregnancy during the height of the 1967 Arab-Israeli “Six-Day” War were significantly more likely to be diagnosed with schizophrenia as adults, they found.

Similar patterns are likely among many stressed women, said Dr. Dolores Malaspina of the New York University School of Medicine, who led the study.

“The stresses in question are those that would be experienced in a natural disaster such as an earthquake or hurricane, a terrorist attack, or a sudden bereavement,” Malaspina said in a statement.

Writing in the BioMed Central journal BMC Psychiatry, the researchers said they studied data from 88,829 people born in Jerusalem from 1964 to 1976.

“The raw data suggest a two- to three-fold excess of schizophrenia in the cohort born in January 1968, whose mothers would have been in the second month of pregnancy in June 1967,” they wrote.

“The population of Jerusalem would have been most stressed during the three days of bombardment on June 5-7.”

Because the war was so short, they consider the situation a natural experiment.

Now the team is looking to see if perhaps people with a genetic predisposition were more or less likely to be affected. It may not necessarily be the case, said Karine Kleinhaus, also of NYU, who worked on the study.

“The hypothesis is that it may induce epigenetic changes, but we didn’t look at blood here,” Kleinhaus said in a telephone interview.

Epigenetic changes affect how a gene works, but not the DNA sequence itself. Schizophrenia, which affects about 1.1 percent of the population globally, is know to have some genetic causes but many cases have no known family links.

“It could affect people without a family history,” Kleinhaus said.

Several studies show that stress in pregnancy can lead to type 2 diabetes, high blood pressure and other types of heart disease in the offspring.

In this study, the effects were seen more in women than in men, with females who had been in their second month of gestation during the conflict 4.3 times more likely to develop schizophrenia than females born at other times. Males were 1.2 times more likely to develop schizophrenia if their mothers were pregnant during the war.

“The placenta is very sensitive to stress hormones in the mother. These hormones were probably amplified during the time of the war,” Malaspina said.

Some evidence suggests that male fetuses are more likely to be miscarried if the mother is stressed, so it may be that female fetuses survive with the damage that eventually leads to schizophrenia, the researchers said. (Editing by Alan Elsner)