Study claims “light drinking” during pregnancy is okay: should one study affect clinical guidelines?

A study released yesterday in the Journal of Epidemiology and Community Health is stirring up a flurry of media attention. Yvonne Kelly (University College London) and colleagues have published a follow-up study to their 2008 paper “Light drinking in pregnancy, a risk for behavioural problems and cognitive deficits at 3 years of age?”

The latest paper examines the relationship between mothers’ self-report of drinking during pregnancy and measures of the social, emotional, and cognitive abilities of their children at age 5 in this same cohort. In both papers, the authors suggest that “light drinking” (defined as 1-2 drinks per week) during pregnancy does not result in harmful effects in children. Further, the findings are framed in such a way that it is suggested that children born to “light drinkers” have better outcomes than children born to “non-drinkers” and that baby boys benefit from light drinking more than baby girls.

I hope you’re all reading this and saying “Hmmm, what could be going on here?” or “Why does this give me a weird feeling?” Some of you might be jumping up and down with alarm bells blaring in the back of your brain which is also an appropriate response.

Well, of course, like any study, there are some methodological concerns. There are also some strengths which I will state up-front. The study involved a large cohort of women from all over the United Kingdom (N=11 513) which is always very helpful when thinking about whether a study applies to the general population in any way. The study also is designed in such a way that it’s possible to look at the effect of other variables that could be affecting the relationship between prenatal alcohol exposure and outcomes.

But, there are also some limitations to this study and it’s these limitations that have direct implications for how seriously this study should be taken in determining policies and guidelines regarding  alcohol use during pregnancy.

  • Mothers were asked to describe their drinking patterns during pregnancy when their baby was 9 months old. If you think this isn’t a problem, try and remember what you ate last week. Not only that, the research literature suggests that the greatest risk from pre-natal alcohol exposure might be in the first trimester of pregnancy. Do you remember what you ate and drank 15 to 18 months ago? And how many women know they are pregnant immediately? Hmmm….
  • The study asked about drinking over the whole pregnancy and didn’t differentiate very well between frequency and amount of drinking. And we know that’s it not just about how much you drink, it’s about when you drink and whether you have one drink every three days or two drinks in one afternoon.
  • The tests used by the researchers to measure cognitive and behavioral outcomes are a lot less sensitive than tests used to assess FASD
  • The relationship between social factors and light drinking are not fully understood. The study does try to address how light drinkers were likely to be older, better educated, from higher income households and less likely to smoke. Social factors like these affect both drinking patterns and the effects of drinking. What might be safe for one social group might not be safe for another social group….

Based on this study alone, I think most researchers would feel comfortable saying that “light drinking” during pregnancy cannot be established as safe. But, it seems from the media response and public discussion that the study really raises two questions:

  1. Should one study influence policy statements regarding drinking during pregnancy?
  2. Should the precautionary principle guide policy decisions?

The study supports “light drinking” and all those who would argue that “moderation in everything” should guide individual decisions. It has been argued that guidelines suggesting abstinence during pregnancy underestimate the public’s ability to make sense of complex relationships and research and that guidelines should reflect the current and ever-changing state of knowledge.

However, I would suggest that the “drinking in moderation” advocates underestimate what is known and understood about the effects of drinking alcohol during pregnancy (the more I read, the more complicated it seems to be) and are suggesting that in the wake of uncertainty more liberal guidelines should be proposed.

The state of the research suggests that “We just don’t know how the amount, timing, and frequency of alcohol consumed during pregnancy affects children.” What we do know is that the effects of prenatal exposure to alcohol can lead to outcomes like Fetal Alcohol Spectrum Disorder. I don’t know about you, but I’d like to err on the side of caution in this particular case.

Read more:


Mom’s light drinking may not harm fetuses, study suggests (The Globe and Mail, Tuesday, October 5, 2010)

Drinking while pregnant: Would a new study change your old perspective? (CBC News, October 6, 2010)

A weekly drink while pregnant does no harm, claims study (Herald Scotland, October 6, 2010)

Read the study abstract below:


Kelly, Y., Sacker, A., Gray, R., Kelly, J., Wolke, D., Head, J., Quigley, M.A. (2010). Light drinking during pregnancy: still no increased risk for socioemotional difficulties or cognitive deficits at 5 years of age? Journal of  Epidemiology and Community Health, doi:10.1136/jech.2009.103002

Background This study examines the relationship between light drinking during pregnancy and the risk of socioemotional problems and cognitive deficits at age 5 years.

Methods Data from the nationally representative prospective UK Millennium Cohort Study (N=11 513) were used. Participants were grouped according to mothers’ reported alcohol consumption during pregnancy: never drinker; not in pregnancy; light; moderate; heavy/binge. At age 5 years the strengths and difficulties questionnaire (SDQ) and British ability scales (BAS) tests were administered during home interviews. Defined clinically relevant cut-offs on the SDQ and standardised scores for the BAS subscales were used.

Results Boys and girls born to light drinkers were less likely to have high total difficulties (for boys 6.6% vs 9.6%, OR=0.67, for girls 4.3% vs 6.2%, OR=0.69) and hyperactivity (for boys 10.1% vs 13.4%, OR=0.73, for girls 5.5% vs 7.6%, OR=0.71) scores compared with those born to mothers in the not-in-pregnancy group. These differences were attenuated on adjustment for confounding and mediating factors. Boys and girls born to light drinkers had higher mean cognitive test scores compared with those born to mothers in the not-in-pregnancy group: for boys, naming vocabulary (58 vs 55), picture similarities (56 vs 55) and pattern construction (52 vs 50), for girls naming vocabulary (58 vs 56) and pattern construction (53 vs 52). Differences remained statistically significant for boys in naming vocabulary and picture similarities.

Conclusions At age 5 years cohort members born to mothers who drank up to 1–2 drinks per week or per occasion during pregnancy were not at increased risk of clinically relevant behavioural difficulties or cognitive deficits compared with children of mothers in the not-in-pregnancy group.