Short-term exposure to alcohol and certain drugs can trigger brain cell death in the foetus, according to new research.
As little as two units of alcohol is enough to speed up brain cell death in foetuses, the study reveals.
The disturbing findings were released at the American Association meeting yesterday during a session looking at the impact of prenatal exposure to alcohol, drugs and environmental toxins.
Two studies in particular showed that alcohol and drug exposure could have a major influence on the developing brain of a foetus, in some cases leading to psychiatric disorders.
Prof John Olney of Washington University, St Louis, described studies of the infant mouse brain and how alcohol and certain anaesthetic drugs could cause brain cells to commit suicide.
"It happens only at a particular time when the nerves are forming their synaptic connections," he told the meeting.
In the human this occurs from the mid-point of gestation and through the first two years of life. Alcohol and certain drugs interfered with the connection process which when thwarted causes the cells to die.
Some anaesthetics such as ketamine are used as recreational drugs or abused together with alcohol, which could have consequences if a woman was pregnant. All of these drugs and others, including anticonvulsives, increased the expected natural nerve cell death between two- and four-fold, Prof Olney said.
"We found that blood alcohol levels produced in the animal that will cause a significant increase in cell suicide, would be the equivalent in human terms of about two cocktails." This achieves a blood alcohol level just below that set for the drunk-drive limit.
It had long been known that high blood alcohol levels could damage the foetal brain, he said. These results were surprising, however, because cell death could also be triggered at comparatively low blood alcohol levels.
Prof Ezra Susser of Columbia University and the New York State Psychiatric Institute discussed his study on how foetal exposure to environmental lead doubled the risk of later developing schizophrenia. "There seems to be no safe levels of exposure to lead," he said.Very low levels cause a similar type of brain cell suicide as alcohol. It is unclear, however, how lead exposure could lead to schizophrenia in some people.