A new UK study that tracked children up to the age of 5, found no evidence that light drinking during pregnancy, that is when their mothers drank no more than one or two units of alcohol a week, harmed their behavioural or intellectual development.
However, government advice that women should avoid alcohol altogether in pregnancy remains in place.
You can read about the study led by University College London (UCL) and involving three other UK research centres, in an online-first paper published in the Journal of Epidemiology and Community Health. The first author is Yvonne J Kelly, a Senior Lecturer in the Epidemiology & Public Health Department of the Division of Population Health at UCL.
An earlier study that followed children up to the age of 3 had already come up with a similar conclusion, that light drinking in pregnancy did not appear to harm children's behavioural and intellectual development, but Kelly and colleagues wanted to rule out possible delayed effects in older children.
For the study, the authors used data from the nationally representative prospective UK Millennium Cohort Study (MCS), covering over 11,500 children born between September 2000 and January 2002.
When the children reached 9 months of age, the researchers interviewed the mothers and assessed their drinking patterns and other socioeconomic factors.
The drinking patterns were classed as: never drinkers, not drinking while pregnant, light drinking during pregnancy (1 or two units a week), moderate drinking during pregnancy (3 to 6 units a week, or 3 to 5 at any one time), and binge/heavy drinking during pregnancy (7 or more units a week or 6 at one time).
This follows the UK government's National Alcohol Strategy categories, which the authors chose to use because there is no widely agreed classification for research.
The mothers were interviewed again when their children reached 3 years of age, this time they answered questions about their children's behaviour.
When the children reached the age of 5, the researchers interviewed them at home and formally assessed their behavioural and congnitive development using the strengths and difficulties questionnaire (SDQ) and British ability scales (BAS).
The results showed that:
- According to information they gave in interviews, 6 per cent of the mothers were classed as never drinkers, 60 per cent as not drinking while pregnant, just under 26 per cent were light drinkers, 5.5 per cent were moderate drinkers, and 2.5 per cent were heavy or binge drinkers during pregnancy.
- Across the whole sample, boys were more likely than girls to have more total developmental problems.
- Boys were also more likely to have behavioural problems, be more hyperactive and have issues with peers.
- However, girls were more likely to have emotional problems.
- Girls attained higher average scores than boys on cognitive tests that covered vocabulary, spotting picture similarities and pattern construction.
- Children of mothers who drank heavily during pregnancy were more likely to be hyperactive, and have behavioural and emotional problems than those whose mothers abstained during pregnancy.
- But in the case of children whose mothers drank only one or two units of alcohol a week during pregnancy, there was no evidence of this being linked to their behavioural or intellectual development.
But Kelly told the press that when they looked more closely at the potential confounders like mother's education level, family income, parental discipline and current drinking habits (the study only assessed drinking in pregnancy), the link was not so strong.
She said this suggests there are probably other factors that have potentially not been accounted for, so the overall message of the study is there was neither benefit nor harm from light drinking, reported The Telegraph.
Kelly emphasized that she and her colleagues was not trying to put across the message that mothers should take up light drinking during pregnancy to improve their child's health.
She said they did not want to get into the "highly political and morally charged debate" around this subject, they just want to report their findings as scientists, which concludes that, compared to children of mothers who abstained from alcohol during pregnancy:
"Children whose mothers reported drinking low levels of alcohol were not at increased risk of difficulties at age five."
A spokeswoman for the Department of Health said they were not updating their guideline issued in 2007 that says pregnant women should avoid alcohol altogether, as should women trying to get pregnant. This replaced previous advice that it was ok for women to drink one or two units a week.
She emphasized that the update was to give women a consistent message and not based on any research. However, even after this latest study, it appears the government is going to stick to the simple message, that women should not drink while pregnant or while trying to conceive.
"After assessing the available evidence, we cannot say with confidence that drinking during pregnancy is safe and will not harm your baby," she said, in a statement reported by the Press Association.
The current advice from NICE, the National Institute of Health and Clinical Excellence, is that women should avoid alcohol in pregnancy, particularly during the first trimester.
Among other experts, advice is also mixed, although all agree that heavy drinking is not alright, whether a woman is pregnant or not.
The Press Association reported that Janet Fyle, a midwife and professional policy advisor at the Royal College of Midwives, said she was concerned that women reading about this study may conclude it is okay to drink while pregnant.
She said there was no "firm evidence" that small amounts of alcohol, which can have a cumulative effect, does not harm the developing unborn baby.
"Because of this our advice to women remains the same; if you are planning to become pregnant, or if you are pregnant, it is best to avoid drinking alcohol," said Fyle.
But the president of the Royal College of Obstetricians and Gynaecologists, Dr Tony Falconer, told the BBC that while not drinking at all while pregnant was the "safest choice", the current evidence suggests drinking one or two units of alcohol a week was alright and that the main message to women should be, whether they are pregnant or not, "light drinking is fine, but heavy and binge drinking should be avoided".
One of the problems surrounding the current debate is that people have different ideas about what constitutes "light drinking".
This was the point made by Chris Sorek, the chief executive of the alcohol awareness charity Drinkaware.
"There is a risk that if pregnant women take this research as a green light to drink a small amount, they could become complacent, drink more than they think they are and inadvertently cause harm to their unborn child," he said.
It is easy to see how this can happen, when one tries to decipher the complexities of how many units there are in a "typical" drink.
In the UK, one unit of alcohol is defined as 10 millilitres of pure ethanol, the alcohol found in alcoholic beverages like wine, beer and spirits.
This means that half a pint (284 ml) of 3.5 per cent alcohol by volume (3.5% abv) beer has almost exactly one unit of alcohol, which is what is often quoted in public health messages. However, in the UK, most beers are stronger than this, so for example a half pint of 5.2% lager is nearly 1.5 units.
There is a similar problem with wines. A small glass (125 ml) of 8% abv wine is one unit, again this is the example often given in public health messages. But in the UK, pubs and restaurants often serve wine in 175 ml and 250 ml glasses, and many wines are stronger than 8% abv.
So, if you go into a pub and order a glass of white wine, you will most likely be given a medium measure (175 ml) of 12% abv wine, which is nearer 2 units of ethanol.
"Light drinking during pregnancy: still no increased risk for socioemotional difficulties or cognitive deficits at 5 years of age?"
Yvonne J Kelly, Amanda Sacker, Ron Gray, John Kelly, Dieter Wolke, Jenny Head, Maria A Quigley.
J Epidemiol Community Health, Published Online First: 5 October 2010
Source: BMJ, Press Association, wikipedia, BBC.
Written by: Catharine Paddock, PhD