Thursday 14 October 2010

Drinking and pregnancy

Light drinking during pregnancy - not more than a drink or two per occassion - has no adverse effects according to the latest at the Journal of Epidemiological and Community Health. Discover and How Stuff Works give decent summaries. From Discover:
The study, which found no evidence of harm from having a couple drinks a week during pregnancy, was so well done and its findings so conclusive that it ought to become the final word in the field, said Fred Bookstein, an applied statistician who studies fetal alcohol spectrum disorders at both the University of Washington, Seattle, and the University of Vienna.

"This is such a good study that it should shut down this line of research," said Boostein, who plans to refer people to the paper when they ask him about drinking during pregnancy, and hopes that research dollars can now go towards finding the effects of other, more troublesome chemicals.

"It is no longer valid to argue that we don't know enough about low-dose drinking during pregnancy or that the known effects of binge drinking may penetrate to low-dose drinkers somehow," he added. "There is no detectable risk associated with light or moderate drinking during pregnancy."
The study design here is better than I've seen in most epidemiological work. They've a panel design where more than eighteen thousand households were interviewed in home visits, with the first visit at child age 9 months and subsequent visits at ages 3 and 5. In the first visit, they asked questions about mothers' drinking during pregnancy as well as about other health-related covariates. At the last visit, the child's cognitive ability and behaviour was assessed. Never-drinking mothers - those who reported no drinking either during pregnancy or in the subsequent periods - were separated from those who only abstained during pregnancy. And they controlled for a reasonably lengthy list of potential confounds beyond the usual sociodemographics: whether the mother smoked during pregnancy, parental disciplining strategies, and so on.

First, some summary data. About eight percent of their sample - just over 900 mothers - reported moderate or heavy drinking during pregnancy. Incidence was slightly skewed towards lower education cohorts, with just over three percent of low education mothers reporting heavy or binge drinking as compared to just over two percent of mothers in the top educational category. Highly educated mothers were the ones most likely to report light drinking during pregnancy, though the modal highly educated mother reported absention during pregnancy. Among the lowest educational cohorts, absention during pregnancy was by far the most likely reported behaviour. So if you're a highly educated mother who sneaks a drink occasionally, you're certainly not alone.

They ran regressions on child outcomes controlling for maternal drinking and for the confounds. The unadjusted data showed massive benefits to being born to a light-drinking mother, but that was mostly due to the confounds; results attenuated in the full models, as you'd expect if it's the higher education parents who are more likely to have a little but not a lot. Controlling for the parental factors didn't reverse the effects, but it really knocked back the magnitude and statistical significance. Typical coefficients on cognitive benefits to the child of the mother's light drinking were knocked back to a third of their baseline magnitude with the full set of controls; it's consequently more than plausible that remaining uncontrolled things that differ between "not during pregnancy" mothers and light-drinking mothers could be responsible for at least some of the remaining gap. An IV strategy would be needed to estimate things more precisely.

But the bottom line seems to be no bad effect, and some (small) chance of a positive effect, of a pregnant woman's drinking up to a drink or two "per week or per occasion" instead of abstaining during pregnancy. I wouldn't bank on the positive effects holding up to an IV model, but I'd also be very surprised if those techniques drove things to a negative effect.

The public healthists' arguments about there not being a safe level really have a feel of the noble lie to them; they seem to fear that admitting a drink or two has no effect would risk opening the door for the binge drinkers to consume up to the point where they could do serious harm.

Dave Guerin also comments, calling the healthists' response "faith based science".

I just wish that Science Media Center would start linking to ungated versions of the articles they're critiquing.


  1. In 1987 and 1989 when I had my first 2 children the advice given was to drink moderately, and that is what I did. By the time I had my third child in 1991 the advice had changed to complete abstention. I ignored this advice (perhaps a little self-servingly), and continued to ignore it until 2004 when I had my 7th child. I was aware all along that there was no evidence that moderate drinking caused any problems, and I resented being told not to drink based on no evidence at all. It was tiresome though, having to put up with the disapproval of other people.

    I had become sceptical of this sort of blanket advice after, with my first 2 children, following advice that babies should be put to sleep on their fronts to lessen the risk of cot death. I did as I was told, in spite of the fact that my instinct was to put them on their backs. Then it transpired that putting babies face down actually increased the risk of cot death, and there had never been any evidence to suggest that it was preventative (someone had extrapolated from a study involving premature babies).

    I am similarly suspicious of current advice that people should not share a bed with their babies. It is deeply instinctive and natural to do this, and I wonder if something that is a risk for a few is being misrepresented as being a risk for everyone.

  2. Seven!! That's awesome. We can barely handle two.

    I really don't know the literature on cot death and bed sharing. Ours stay in their beds as much as possible, mostly to save our sanity.