Severe stress during the early months of pregnancy can lead to a significantly increased risk of giving birth to a child who develops schizophrenia, a study has suggested.
Researchers used data from the children of women who were in Israel during the 1967 Six Day War, and found they had a much greater propensity to the psychotic disorder over the next 21 to 33 years.
Following the Arab-Israeli war, women who had been in their second month of foetal life during the conflict were 4.3 times more likely to develop schizophrenia than those born at other times. Men in the same situation had a 1.2 times increased risk of the mental illness.
Study leader Dr Dolores Malaspina, from the New York University School of Medicine, said: "It's a very striking confirmation of something that has been suspected for quite some time.
"The placenta is very sensitive to stress hormones in the mother. These hormones were probably amplified during the time of war."
The researchers, whose findings are published in the journal BMC Psychiatry, studied the medical records of 88,829 people born in Jerusalem between 1964 and 1976.
Individuals most likely to develop schizophrenia were in their second month of pregnancy during the height of the conflict in June 1967.
Dr Malaspina said women should not be worried about suffering day-to-day stress during pregnancy. "Women experiencing anxiety or excessive stress would do well to address it before a planned pregnancy and to have good social support systems."
Schizophrenia, marked by delusional thinking, hallucinations and the risk of suicide, affects about 1% of the population. It most commonly emerges in people between the ages of 15 and 35.