Friday September 12 2014
It's best not to drink any alcohol when pregnant
“Binge drinking ONCE during pregnancy can damage your child's mental health and school results,” says the Mail Online.
The headline follows an analysis of results from a study including thousands of women and their children. In analyses of up to 7,000 children, researchers found that children of women who engaged in binge drinking at least once in pregnancy, but did not drink daily, had slightly higher levels of hyperactivity and inattention problems. These children also scored on average about one point lower in exams.
The results appear to suggest potential for some links, particularly in the area of hyperactivity/inattention. However, the differences identified were generally small, and weren’t always statistically significant after taking into account potential confounders. The links also weren’t always found across both boys and girls, or across both teachers’ and parents’ assessment of the child.
It’s already official advice for women to avoid binge drinking or getting drunk when pregnant. Pregnant women should avoid alcohol in the first three months of pregnancy, especially. If women choose to drink alcohol, officials say to stick to, at most, two units (preferably one) and no more than twice a week (preferably once).
Where did the story come from?
The study was carried out by researchers from the University of Nottingham and other research centres in the UK and Australia. The ongoing study is funded by the Medical Research Council, the Wellcome Trust and the University of Bristol. The study was published in the peer-reviewed European Journal of Child and Adolescent Psychiatry.
The media covers the research reasonably, although they sometimes refer generally to the effect on children’s mental health, which may make readers think they are referring to diagnoses of mental health conditions, which is not the case.
The study looked at teacher- and parent-rated levels of problems in areas such as “hyperactivity” and conduct, but did not assess whether the children had psychiatric diagnoses, such as ADHD.
What kind of research was this?
This research was part of a cohort study. The current analysis looked at the effect of binge drinking in pregnancy on mental health and school achievement when the children were aged 11. ALSPAC researchers recruited 85% of the pregnant women in the Avon region due to give birth between 1991 and 1992. Researchers have been assessing these women and their children regularly.
The researchers reported that previous analyses of this study have suggested that there was a link between binge drinking in pregnancy and the child having poorer mental health at ages four and seven as rated by their parents, particularly girls.
A prospective cohort study is the most appropriate and reliable study design for assessing the impact of binge drinking in pregnancy on the child’s heath later in life. For studies of this type, the main difficulty is trying to reduce the potential impact of factors other than the factor of interest (binge drinking) that could affect results. The researchers do this by measuring these factors and then using statistical methods to remove their effect in their analyses. This may not entirely remove their effect, and unknown and unmeasured factors could be having an effect, but it is the best way we have to try and isolate the impact of interest alone.
What did the research involve?
The researchers assessed the women’s alcohol consumption by questionnaire at 18 and 32 weeks into their pregnancy. They assessed their offspring’s mental health and school performance at age 11 using parent and teacher questionnaires, and their academic performance. They then analysed whether children of mothers who had engaged in binge drinking during pregnancy differed to children of mothers who had not.
Of the over 14,000 pregnant women in the study, 7,965 provided information on their alcohol consumption at both 18 and 32 weeks. They were asked about:
- how many days in the past four weeks she had drunk at least four units of alcohol
- how much and how often they had drunk alcohol in the past two weeks or around the time the baby first moved (only asked at 18 weeks)
- how much she currently drank in a day (only asked at 32 weeks)
The researchers used this information to determine if the women:
- had engaged in binge drinking at least once in pregnancy (defined as four or more units/drinks in a day)
- drank at least one drink a day at either 18 or 32 weeks
The children’s mental health was assessed using a commonly used standard questionnaire given to teachers and parents. This questionnaire (called the “Strengths and Difficulties Questionnaire”) gives an indication of the level of problems in four areas:
- peer relationships
The Strengths and Difficulties Questionnaire also gives an overall score, and this is what the researchers focused on, as well as the conduct and hyperactivity/inattention scores. The researchers also obtained the children’s results on standard Key Stage 2 examinations taken in the final year at primary school. The researchers had information on 4,000 children for hyperactivity and conduct problems, and just under 7,000 children for academic results.
When the researchers carried out their analyses to look at the effect of binge drinking, they took into account a range of factors that could potentially influence results (potential confounders). These included:
- mother’s age in pregnancy
- parents’ highest education level
- smoking in pregnancy
- drug use in pregnancy
- maternal mental health in pregnancy
- whether the parents owned their house
- whether the parents were married
- whether the child was born prematurely
- the child’s birthweight
- the child’s gender
What were the basic results?
The researchers found that about a quarter of women (24%) reported having engaged in binge drinking at least once in pregnancy. Over half (59%) of the women who reported binge drinking at 18 weeks in their pregnancy also reported having engaged in binge drinking at 32 weeks.
Less than half of the women (about 44%) who had engaged in binge drinking reported doing so on more than two occasions in the past month. Women who had engaged in binge drinking were more likely to have more children, to also smoke or use illegal drugs in pregnancy, to have experienced depression in pregnancy, to have a lower level of education, to be unmarried and to be in rented accommodation.
Initial analyses showed children of mothers who had engaged in binge drinking at least once in pregnancy had higher levels of parent- and teacher-rated problems, and worse school performance than children of mothers who had not engaged in binge drinking. Their average difference in three problem scores was less than one point (possible score range 0 to 10 for conduct and hyperactivity/inattention problems, and 0 to 40 for the total problems score), and their average KS2 score was 1.82 points lower.
However, once the researchers took into account potential confounding factors, these differences were no longer large enough to rule out the possibility of having occurred by chance (that is, they were no longer statistically significant).
The researchers repeated their analyses for girls and boys separately. They found that even after adjustment, girls whose mothers had engaged in binge drinking in pregnancy did have higher levels of parent-rated conduct, hyperactivity/inattention and total problems (average score difference less than one point).
If the researchers looked at binge drinking and daily drinking separately, after adjustment they found children of women who had engaged in binge drinking in pregnancy, but did not drink daily, had higher levels of teacher-rated hyperactivity/inattention problems (average score 0.28 points higher) and lower KS2 scores (average 0.81 points lower).
How did the researchers interpret the results?
The researchers concluded that occasional binge drinking in pregnancy appears to increase risk of hyperactivity/inattention problems and lower academic performance in children at age 11, even if the women do not drink daily.
This prospective cohort study has suggested that even occasional binge drinking in pregnancy may increase the risk of hyperactivity/inattention problems and lower academic performance when the children reach 11 years old.
The strengths of the study are its design – selecting a wide and representative population sample collecting data prospectively – and using standardised questionnaires to assess the children’s outcomes.
Assessing the impact of alcohol in pregnancy on children’s outcomes is difficult. This is partly because assessing alcohol consumption is always difficult. People may not want to report their true consumption, and even if they do, there are difficulties in accurately remembering past consumption. In addition, as this link can only be assessed by observational studies (ethically you couldn’t do a trial that randomised pregnant women to binge drink), it is always possible that additional factors are having an effect.
The study found that women who had engaged in binge drinking in pregnancy were also more likely to have other unhealthy behaviours, such as smoking, and to be socioeconomically disadvantaged. The researchers tried to remove the effects of all of these factors, but this may not entirely remove the effect.
This latest study carried out a large number of analyses looking at different outcomes. The differences identified were generally small, and they weren’t always large enough to be statistically significant after taking into account potential confounders. They also weren’t always found across both boys and girls, or across both teachers’ and parents’ assessment of the child. These differences weren’t always large enough to be statistically significant. However, they do appear to suggest potential for some links, particularly in the area of hyperactivity/inattention.
The researchers note that even with small individual effects, the effect across the population as a whole can be considerable. The small effect may also reflect that it represents an average effect across all levels of binge drinking – ranging from one to many times.
We may never have completely concrete proof of an exact level at which harm occurs, and under which alcohol consumption in pregnancy is safe. Therefore, we have to work with the best information that is available. There is growing evidence that as well as how much we drink, the pattern of how we drink may be important.
Current UK recommendations from the National Institute for Health and Care Excellence (NICE) already advise that women who are pregnant should avoid binge drinking or getting drunk. It is also recommended that:
- women who are pregnant should avoid alcohol in the first three months of pregnancy
- if women choose to drink alcohol later in pregnancy, they should drink no more than two (preferably only one) UK units, no more than twice (preferably once) a week.
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter. Join the Healthy Evidence forum.