Friday October 31 2008
Babies born to mothers who drink alcohol during pregnancy suffer no harm and ‘may even benefit’, according to news reports today.
The Times refers to the "Blessing of a weekly tipple in pregnancy,” while the Daily Express suggests that wine in pregnancy can control child behaviour.
In fact, the study the stories are based on found no benefits of low levels of alcohol in pregnancy. And while the study found no evidence of harm, it was designed in a way that meant it could not show for sure that light drinking in pregnancy is harmless.
Current NHS advice is to avoid drinking during pregnancy, but if women choose to drink they should have no more than one or two units once or twice a week.
There are known risks associated with heavy drinking during pregnancy, and given the uncertainty, pregnant women might want to err on the side of caution and avoid alcohol during pregnancy.
Where did the story come from?
Dr Yvonne Kelly and colleagues from University College London, the University of Essex and Warwick Medical School carried out this study. It was published in the peer-reviewed medical journal, International Journal of Epidemiology.
What kind of scientific study was this?
This publication was based on analysis of data from a cohort study – the Millennium Cohort Study (MCS) Researchers looked at the link between mothers’ drinking during pregnancy and the results of cognitive testing in children aged 3 years.
The Millennium Cohort study includes a sample of infants born in England and Wales between September 2000 and August 2001, and in Scotland and Northern Ireland between November 2000 and January 2002. Households were interviewed for the first time when babies were 9 months old and at this point interviewers asked how often they drank during pregnancy and also how much was drunk.
Using this information, drinking was categorised as ‘never’, ‘light, not more than 1 to 2 units per week or per occasion’, ‘moderate, not more than 3 to 6 units per week or 3 to 5 units per occasion’, ‘heavy/binge, 7 or more units per week or 6 or more units per occasion’. They also asked about other health-related behaviours, social and economic details, and details about household composition.
A second round of interviews occurred when the child was three years old and at this time the interviewers performed cognitive tests on the child and asked questions about behaviour, social and economic factors and the psychological and social environment of the family. Parents also completed a questionnaire called the Strengths and Difficulties Questionnaire which is often used to assess behavioural problems.
White babies who were not twins, whose mothers had participated in the first two interviews of the MCS study were included in the analysis. This amounted to 12,495 children but about a quarter of the records had some information missing , so the final analyses was of about 9,000 children.
The analyses of the link between drinking during pregnancy and behavioural outcomes (total difficulties, conduct problems, hyperactivity, emotional symptoms, peer problems) at age three years took into account other factors that may affect the link, such as gender, and social and economic status. Boy and girl babies were analysed separately.
What were the results of the study?
The majority of women reported abstaining from alcohol during pregnancy (63%); 29% were ‘light’ drinkers while 6% and 2% were moderate and heavy/binge drinking. Compared with abstainers they also found that ‘light’ drinkers were more likely to be better educated, from higher income households and were less likely to have smoked during pregnancy.
Boys were more likely than girls to show 'high difficulty' behaviour. Mothers’ occupation and social and economic status were also related to child behaviour.
The effects of light drinking compared to abstaining were statistically significant only in two behavioural measures with boys and none with girls. Boys born to light drinkers were les less likely to have conduct problems or to be hyperactive.
What interpretations did the researchers draw from these results?
The researchers conclude that children born to mothers who drank up to 1 to 2 drinks per week or per occasion during pregnancy were not at increased risk of behavioural difficulties or cognitive deficits compared to mothers who didn’t drink anything during pregnancy. They say that while heaving drinking appears to be linked to behavioural problems at age three years, light drinking does not.
What does the NHS Knowledge Service make of this study?
This study – which analysed data from a large, ongoing cohort study – has concluded that light drinking doesn’t appear to lead to poorer cognitive or behavioural outcomes for children compared with no drinking. The study must be interpreted in light of the limitations associated with its methods:
- Importantly, data on miscarriages, stillbirths and neonatal deaths were not captured by the MCS. This is important because drinking during the first three months of pregnancy may increase the risk of miscarriage.
- Other factors that the researchers dfid not account for may have affected behaviour.
- Mothers themselves reported how much they drank. Because drinking alcohol during pregnancy is disapproved of, some women may have chosen not to give full details of their drinking.
- Mothers reported their drinking during pregnancy 9 months after birth., and may not have remembered how much they drank up to 18 months earlier.
- Women whose children had behavioural problems may have reported drinking habits in a different way to other mothers.
- There is a wide range of drinking habits included in the ‘light’ drinking category from one or two drinks during the whole pregnancy to two drinks a week for the whole pregnancy. This makes it difficult to draw conclusions about what ‘light’ means and how much the women in this category were actually drinking.
- ‘Light’ drinking may indicate particular social circumstances in which children are brought up. In this study ‘light drinkers’ were more likely to be from higher socioeconomic classes. It may be social circumstances that lead to improved behaviour and not drinking.
- The design of this study means it cannot rule out other factors that may be responsible for the behavioural differences between ‘light’ drinkers and abstainers.
Ultimately it is the choice of each pregnant woman whether to drink or not and those that choose to will have been officially advised to drink no more than one or two units once or twice a week.
Official advice regarding drinking during pregnancy should not be ignored on the basis of this study. As there are known risks associated with heavy drinking during pregnancy and given that it is difficult for studies to determine what lower limit is safe, women might choose to avoid alcohol during pregnancy.
Sir Muir Gray adds...
The evidence still suggests that no alcohol is a sensible choice for pregnant women.