Just a hunch (the trouble with what everyone “knows”)

Those of you who’ve been reading this blog for a while know that what one “can” and “can’t” do during pregnancy is one of my favorite topics. Much of this is based on nothing that resembles scientific evidence; the old prescriptions about exercise during pregnancy were, in some cases, based on small studies of pregnant ewes stuck on treadmills.

The research community knows this (and Annie Murphy Paul’s new book, Origins, covers the fascinating new field of fetal research), but information trickles down to primary care providers very slowly. The first doctor I saw when I was pregnant with Jasper informed me that I shouldn’t run past 18 weeks and that I had to keep my heart rate under 140 beats per minute (which hasn’t been the guideline in years). It seemed like common sense that vigorous exercise would be dangerous for the baby. All that bouncing around! The trouble with this “common sense,” though, is that it discourages women from exercising. And when pregnant women don’t exercise, they gain too much weight. And when they gain too much weight, they put themselves and their babies at greater risk for a lifetime of medical ills than you’d risk by running 2-3 miles, 5 times a week.

Now, some new research is showing that this same bias toward “better safe than sorry” is troublesome when it comes to drinking during pregnancy too. A new study published this week in the Journal of Epidemiology and Community Health finds that, when looking at more than 18,000 children born between 2000 and 2002 in the UK, children of binge drinkers and children of teetotalers had almost equally bad outcomes. The study found no evidence that light drinking causes emotional or learning problems up to age 5. And as Discovery News reports, “In some tests of vocabulary and pattern creation, boys actually did best if their moms drank a little while carrying them. The findings confirmed what the researchers had found when the kids were three years old.”

Why might a little alcohol be beneficial? The lead researcher at University College London postulated that perhaps a little alcohol helps the mom-to-be relax. Pregnancy is a stressful time, and one of the new insights from fetal research is that too many stress-induced chemicals actually can harm a fetus. But the point of this is that there is no reason to tell pregnant women not to drink at all, and certainly no reason for bars to refuse to serve pregnant women (as Babble covers).

While writing 168 Hours, I became aware of just how powerful, and yet incorrect, many of our “hunches” are. For instance, we believe that it must be true that children do better if a parent stays home with them — particularly babies. And yet recent research from Columbia University shows that this isn’t necessarily true. Data from time diary studies reveals why this might be; mothers who are in and out of the work force don’t spend dramatically different numbers of hours per week interacting with their children. Plus two incomes confer a financial advantage that translates into good outcomes.

We also assume that parents of young kids are chronically sleep deprived. Yet the American Time Use Survey finds that even moms and dads who work full time, and have kids under age 6, average more than 8 hours per every 24 hour period.

There are all kinds of examples of this. Po Bronson and Ashley Merryman write in NurtureShock about a study that had well-to-do kids keep a gratitude journal, apparently to make them happier. ‘The gratitude journal sounded like exactly the sort of exercise kids should do. Everyone involved wanted it to work and fully expected it to work,” they write. But the results, though covered widely, were quite flimsy. Just because something is common sense doesn’t mean it’s correct. Common sense, like everything, should be questioned. (Now that’s an idea to drink to).


2 thoughts on “Just a hunch (the trouble with what everyone “knows”)

  1. Hi Laura,
    Just a little science reporting peeve. Your opening paragraph makes it sound as though doing a small study or using a study about a different mammal to draw conclusions about humans (pregnant women in this case) is less than scientific. The very research scientists who you claim know better do actually use these methods and they do it for highly scientific reasons.

    First, it’s not considered ethical to do randomized studies on pregnant women. So they either do observational studies and control for selection effects (a certain type of woman is more likely to exercise) or they do randomized studies in other organisms (mice or pigs or in this case ewes) in which they believe the mechanism is similar. This goes for heart, lung, kidney and other studies too. The reason the ewe study was wrong was because the relationship between pregnancy and exercise is different in humans. But that’s not always so.

    Second, small sample studies are not inherently invalid. The problem with small samples is that it’s hard to assume that the observations are normally distributed around the mean. However, if the researchers can demonstrate why that assumption holds or why it doesn’t matter, there’s no reason why their conclusions should be ignored. Also, in a smaller sample, the hurdle for stating that an effect is statistically significant has to be higher. Small samples also allow researchers to do matched pair designs or examine counterfactuals that allow them to refine their theory of how the mechanism works, even if they don’t find a significant result.

  2. Doctors in England used to prescribe Guinness for pregnant women, because it was so nutritious–I don’t know if they still do. When my mom was nursing me and my brother, La Leche League advised nursing mothers to drink imported beer because the alcohol would help bring their milk down (through relaxation) and for the nutritional value of the live yeast. (This was before the rise of American microbrewing, so at the time there were no domestic beers that contained live yeast.) Since adults who drink moderately live longer and are healthier than teetotalers or binge drinkers, it makes sense that would apply to babies too. That it’s taken this long to be studied or get any press suggests that American attitudes toward alcohol mix up science with morality more than other countries do.

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