The new research, published in the British Medical Journal, also suggests that males whose mothers have had at least three previous children may be at greater risk of developing the condition.

The link is weaker for female children.

A team of scientists from Europe and Japan has found that the development of schizophrenia is associated with underweight foetuses and with bleeding during pregnancy.

They suggest that reduced placental function may subtly impair foetal brain development, leaving the individual more vulnerable to later schizophrenia.

The researchers found only a much weaker link between problems in pregnancy and other types of psychotic illnesses.

Step forward

Low weight foetuses may be at risk

Reviewing the research in a BMJ editorial, John Geddes, of the University Department of Psychiatry at Warneford Hospital, Oxford, said researchers had been reporting a link between childbirth and schizophrenia for three decades.

But he said the new research was a major improvement on previous studies, which were of dubious quality and clouded by the suspicion that there was bias towards publication of positive findings.

He said: "It is larger than previous studies, the analyses are straightforward, and interpretation is appropriately cautious."

However, he said there was still considerable uncertainty about the underlying mechanism that might lead to the development of schizophrenia.

A spokesman for the National Schizophrenia Fellowship said: "Schizophrenia is a very complex subject. There is no general medical agreement about whether it is one illness or a number of different illnesses, and trying to pinpoint one cause would be very difficult indeed."

Dr Matt Muijen, director of the Sainsbury's Centre for Mental Health, said it was likely that schizophrenia was caused by a complex combination of genetic and environmental factors.

He said: "This is interesting research, which makes us think.

"However, I doubt whether birth complications could explain more than a few per cent of cases of schizophrenia - if it was a simple as that we could have known it by now."

A Canadian study published last November found that children born by Caesarean section could be more likely to develop schizophrenia.