Comment »Posted on Monday 3 November 2008 at 2:35 pm by Jacob Aron
In Biology, Getting It Wrong

Research published last week in the International Journal of Epidemiology suggests that mothers who drinking “lightly” during pregnancy are not putting their unborn child at risk of behavioural difficulties or cognitive deficits, when compared with children of abstinent mothers. In some cases, light drinking was actually shown to be beneficial, according to lead author Dr Yvonne Kelly of University College London’s Epidemiology & Public Health department:

“The link between heavy drinking during pregnancy and consequent poor behavioural and cognitive outcomes in children is well established. However, very few studies have considered whether light drinking in pregnancy is a risk for behavioural and cognitive problems in children.

“Our research has found that light drinking by pregnant mothers does not increase the risk of behavioural difficulties or cognitive deficits. Indeed, for some behavioural and cognitive outcomes, children born to light drinkers were less likely to have problems compared to children of abstinent mothers, although children born to heavy drinkers were more likely to have problems compared to children of mothers who drank nothing whilst pregnant.”

The study defines light drinking as 1-2 units of alcohol per week or occasion. This confuses me; what counts as an occasion? If a mum-to-be likes to party every day of the week, does this mean that she’s fine as long as she restricts herself to 1-2 units each night? Of course not, so why not just stick to the amount consumed per week?

I worry that this confusion could be spread to pregnant women by the reporting of the story in the mass media. The stated 2 units amounts to a single 175ml glass of wine of around 11% alcohol strength per week. Personally I would consider this “barely” rather than “light” drinking, which to me seems more like two or three glasses of wine week for a total of 4-6 units per week – still well under the recommended limit of 14 units per week for women. I wonder how many women might have a similar interpretation of “light”, and drink too much after reading this story.

The Times were the most cautious in their reporting, with “Drinking alcohol occasionally when pregnant ‘does no harm’“, and in the second paragraph define “occasionally” as “one to two units, or a single drink a week”. You’d be hard pressed to come away from reading their story thinking a bit of a binge would be ok.

Similarly, the BBC said “Light drinking ‘no risk to baby’“, but said that the study defined “light” as “two drinks a week”, not 2 units. The study itself is unclear on this matter, sometimes switching between 2 units and 2 drinks. I can’t think of any reasonably sized serving in which 1 unit = 1 drink. For the calculations to work out, we’re talking a measly 100ml of 10% strength wine. I think you’d be hard pressed to find anyone who defined such a measure as a “drink”.

The Telegraph falls somewhere in the middle with “Pregnant women ‘can drink a small glass of wine a week’” – a decent headline, but they go on to say “Guidelines on what constitutes a unit has since been changed and only a small (125ml) glass of 12% ABV white wine is the equivalent to one unit.” I’m not sure what guidelines they are referring to – one unit is 10ml of pure alcohol, so their example would be (125 * 0.12) / 10 = 1.5 units. In other words, women following the Telegraph’s advice might be at risk of drinking more than 2 units.

Finally, both the Guardian (Light drinking in pregnancy may be good for baby boys, says study) and the Daily Mail (Pregnant women who drink ‘lightly’ could have brighter, better-behaved babies) were perhaps overly optimistic in their reporting of the study, stressing the potential positive benefits. This stance makes for good headlines, but could it mean women don’t think twice before reaching for another glass – after all, it might even be good for the baby!

Ultimately I blame the press release from UCL which went with the headline “Light drinking in pregnancy not bad for children, says UCL study“. Even though the first line immediatly defines the meaning of “light”, it’s just encouraging over-confident reporting by the newspapers. After all, that’s pretty much the point of these press releases – enticing science writers to cover the latest breakthrough. Journalists love an eye-catching headline as much as any reader.

Scientists use very exact language for a reason: if you don’t, it gets you in to trouble. It’s very hard to reproduce someone’s results if their methodology is written like a cook-book (“take a pinch of copper, add a dash of hydrochloric acid…”), so being specific is important. When stories get picked up by the mass media, these specifics are often lost or glossed over – after all, no one really cares how many protons are in a carbon nucleus (for example) other than scientists, right?

The trouble is, when it comes to research such as this, the specifics are pretty important. If your definition of “light” drinking is different to that of the study’s authors, the university press officers, or the newspaper editors, you could be putting your baby at risk. Sometimes it’s ok to dumb down the science, and sometimes it really isn’t.


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