Women who endure severe stress early in pregnancy may be more likely to have children that go on to develop schizophrenia, research suggests.
The first three months of pregnancy seem key
A University of Manchester team looked at data from 1.38 million Danish births occurring between 1973 and 1995.
The risk of schizophrenia and related disorders was around 67% greater among the offspring of women who lost a relative during their first trimester.
The study appears in the journal Archives of General Psychiatry.
The findings appear to confirm the theory that a mother's psychological state can have a profound influence on her unborn baby.
Previous research has linked stress in pregnancy to a raised risk of low birth weight and prematurity.
And some studies have also suggested that the abnormalities in brain structure and function that are associated with schizophrenia may begin to form in the earliest stages of development.
However, the researchers found no evidence that a loss of a relative at any other time during the pregnancy, or in the six months leading up to a pregnancy, had any effect on the unborn baby.
In addition, the association between bereavement and schizophrenia risk only appeared significant for people without a family history of mental illness.
The researchers suggest that chemicals released by the mother's brain in response to stress may have a direct impact on the foetus's developing brain.
These effects may be strongest in early pregnancy, when protective barriers between the mother and foetus are not fully constructed.
They add that the risk of schizophrenia is likely to be influenced by other factors, such as genes.
Researcher Professor Philip Baker, an obstetrician at St Mary's Hospital Manchester, said: "Increasingly we are learning that the environment a baby is exposed to inside the womb is determining long-term health."
However, he added: "We don't want to over-worry people because the absolute risks are small."
Paul Corry, of the mental health charity Rethink, said research had thrown up a lot of possible risk factors for schizophrenia.
"We know that the field of genetics and mental illness is poorly funded and this research shows why this needs to be corrected.
"It is only by following up leads, however tentative, that we will come to a better understanding of the causes and, from there, better care and treatment of devastating illnesses like schizophrenia."