Up to 17% people in the United Kingdom could have symptoms of foetal alcohol spectrum disorder (FASD) because their mothers drank during pregnancy, a study has found.
The lifelong condition is caused by exposure to alcohol in pregnancy and affects learning and behaviour.
It can cause physical abnormalities including distinctive facial features such as a small head and eyes.
The research, published in the journal Preventive Medicine, was collated from an on-going study which looked at the records of women who were pregnant between 1991 and 1992.
Researchers from the University of Bristol and Cardiff University followed the development of 13,495 children from birth until the age of 15.
The UK has the fourth highest level of pre-natal alcohol use in the world but the research is the first to estimate how many people may have FASD, which has previously thought to be under-diagnosed.
Dr Cheryl McQuire, researcher in epidemiology and alcohol-related outcomes at the University of Bristol, who led the research, said:
“The results are based on a screening tool, which is not the same as a formal diagnosis.
“Nevertheless, the high rates of prenatal alcohol use and FASD-relevant symptoms that we found in our study suggest that FASD is likely to be a significant public health concern in the UK".
A positive FASD screen was defined as problems with at least three different areas of learning or behaviour, with or without physical anomalies.
These anomalies include growth deficiency and distinctive facial features, such as a thin upper lip and small eye openings.
Results from these have concluded that 10% of children in the general population are affected, with rates as high as 30% for those in care, Dr McQuire said.
Dr McQuire said the results were important in order to raise awareness of FASD so people with the condition could get the support they needed.
The research, which used data from the Children of the 90s study in Bristol, found up to 79% of children were exposed to alcohol in the womb.
Campaigners welcomed the study, saying the condition was one that could no longer be ignored.
Dr Raja Mukherjee, who runs a diagnostic clinic for FASD at Surrey and Boarders Partnership NHS Foundation Trust, said: "These are really important results that show there are likely to be many individuals with this disorder already out there who are being missed.
"There seems to be a disconnect between these findings and what many clinicians often report as a rare condition.
"If we fail to diagnose it then those affected individuals will continue to be affected by a lack of support and have subsequent impact on them and wider service."
Sandra Butcher, chief executive of NO-FAS UK, a charity to help those affected, said more support was needed "on every level".
But the British Pregnancy Advisory Service (bpas) advised caution on the results, saying that they could cause "needless anxiety" in pregnant women.
Clare Murphy director of external affairs at bpsa said the results should not be considered definitive: “We advise real caution over the interpretation and communication of these findings.
“This study, as the authors themselves acknowledge, does not prove any causal link between pregnancy drinking and the developmental outcomes recorded, and may cause pregnant women and parents needless anxiety.”
Advice from the chief medical officers for the UK states that women who are pregnant, or think they could become pregnant, should not drink alcohol at all to keep risks to the baby to a minimum.
It advises that the risk of harm is likely to be low if women have only drunk small amounts before they knew they were pregnant, or during pregnancy.
Women who have consumed alcohol in early pregnancy should avoid further drinking, though the risks to their baby are likely to be low.
The Children of the 90s study, also known as the Avon Longitudinal Study of Parents and Children (ALSPAC), is a long-term health research project.
It enrolled more than 14,000 pregnant women in 1991 and 1992 and has been following the health and development of the parents and their children ever since.