Women who consume alcohol or drugs during pregnancy could do permanent damage to their unborn child, according to the first-ever long-term study into the issue.
Researchers at Zurich University and in Germany have published their findings into fetal alcohol syndrome (FAS).
Nearly 40 individuals with FAS or FASD (fetal alcohol syndrome spectrum disorder) were followed over a 20-year period, from early childhood.
The results, published in the Journal of Paediatrics, found while some physical problems such as cranial and facial deformities can improve over time, men whose mothers had consumed alcohol remained underweight while women often stayed overweight.
And Professor Hans-Christoph Steinhausen at Zurich University, in collaboration with Berlin paediatrician Hans-Ludwig Spohr, was for the first time able to present evidence that "intellectual and behavioural problems persist and prevent most of the individuals from successfully working or living independently".
Many retained mental disabilities which limited their employment opportunities and therefore kept them dependent on social services for their welfare.
The researchers cautioned that it was not yet possible to determine the level of alcohol that caused damage to an unborn child, but recommended that women limit their consumption to no more than one glass a day.
Steinhausen and his colleagues also investigated the impact of illicit drug consumption, working with drug addicts taking part in a Swiss treatment programme and their offspring.
Tests found that the intelligence levels of children of substance-dependent mothers were significantly lower than the Swiss average and "there was an excess of children with subnormal intellectual functioning".
Biological and psychosocial risks were taken into account to see if these were factors in the children's development. These included the mother's social network, characteristics of her addiction, as well as her own intelligence and psychological state.
While a lack of a support group, low level of education and mental disorders in the women contributed to their children developing behavioural problems, it was discovered that substance abuse in the prenatal phase, predominately use of heroin or methadone, was the only factor that had a negative effect on IQ.
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FAS and FASD
It's believed that alcohol crosses the placental barrier, stunting fetal growth and weight, disfiguring facial features and damaging brain structure.
Developing brain cells and structures are underdeveloped or malformed, often creating cognitive or functional disabilities such as poor memory and attention deficit disorder.
Fetal Alcohol Spectrum Disorder goes beyond FAS to describe a continuum of permanent birth defects resulting from prenatal alcohol exposure, including physical, behavioural and cognitive.