One media-blasted notion that most women now seem to take at face value is the importance of not drinking a drop of alcohol during pregnancy. The most ironic part of the propoganda is that those passing it along know it is a double-edged sword: they try to keep an impossible balance between convincing you that one beer will cause irreparable harm to your fetus, and assuring you that if you had some drinks before you were pregnant, you shouldn't acutally worry.

This contradiction might make some women wonder where the truth lies. While it is clear that excessive alcohol consumption can result in Fetal Alcohol Syndrome (FAS), a suite of birth defects mainly affecting the brain (learning and memory), but Wikipedia's definition of the condition is misleading in that it states: "It is unknown whether amount, frequency or timing of alcohol consumption during pregnancy causes a difference in amount of damage done to the fetus." A perusal of the current literature on the topic of alcohol and pregnancy makes it quite clear that generally there is a positive relationship between the amount of alcohol consumed during pregnancy and the likelihood and severity of defects. In addition, it is also known that the most important brain development occurs in the first trimester, and thus that is almost certainly the most critical period to avoid consumption of alcohol.

What has been unknown since the FAS-prevention media blitz started is whether or not there is a threshold level of alcohol consumption below which there is no damage to the child. Frankly, there doesn't seem to have been a lot of interest in this among medical professionals, because it is simpler just to tell women not to drink at all than it is to consider nuances that might cause women to think it is okay to drink, and then drink too much, whatever too much is. The one certainty is that if a woman does not drink at all, there is no danger of impairments to the fetus caused by alcohol.

There have been occasional papers, however, focusing on the moderate drinkers, in order to possibly establish a safety threshold for alcohol consumption. One research project in particular is interesting because it is an ongoing longitudinal study that began when 580 mothers involved joined the study at 4 months pregnant. The most recent paper I was able to access on the study has data from when the focal children were 14 years old (Wilford, J.A., Richardson, G.A., Leech, S.L., Day, N.L., 2004. Verbal and visuospatial learning and memory function in children with moderate prenatal alcohol exposure. Alcoholism: Clinical and Experimental Research. 28:497-507.) This study is a genuine attempt to uncover potentially subtle effects on children whose mothers had around three drinks or less a week during pregnancy.

The positive aspects of the paper is that 1) it separates drinking by trimester, which is developmentally relevant and 2) it compares continuous variables in a regression analysis - e.g. drinking amounts are not placed into arbitrary categories, rather the actual volume drunk is used for the data.
The problems with the paper are pretty much the same ones that plague so many medical papers. First, by necessity, drinking levels are self-reported. Given that the first assessment was at 4 months - after the first trimester - the accuracy of the data is not convincing. Not only was each woman required to remember amounts drunk months previously (questionable even for those not experiencing the undulating body chemistry of pregnancy) but at the point these women were pregnant there was already some media blitzing discouraging drinking during pregnancy. The authors do not address the problem of potential underreporting bias.

Mainly, though, the problems are statistical. The authors used a large suite of learning and memory tests to score the children. They then regressed every variable they could think of against the scores, because of the need to correct for all the other potential factors influencing the scores, for example: race, mother's IQ, child's age, child's current substance use, mother's current substance use, etc. in addition to mother's alcohol and other substance use over each trimester. This makes for an extremely large number of statistical tests performed, although the number is unreported and thus must be estimated. The "significant" results alone number 31. For the six learning and memory tests that had "significant" results, all included mother's use of alcohol in the first trimester (but not the second or third in any case). This leads to a long discussion of the mechanism by which moderate drinking has caused "learning and memory deficits" in these children, etc.

But assuming the learning and memory tests are valid evaluations, we need to take another look at what the statistics actually showed. (Table 2 with p-value results is reproduced below.) First of all, one of the most basic statistical rules, ignored by doctors in every case I have seen, is that there is a probability of being wrong about the result. It is generally accepted that if the statistics show 95% probability of an effect, it is a valid result. The problem arises when as part of a single study, a large number of statistical tests are run, as in this case. The flip side of being 95% sure is that out of every 20 statistical tests conducted, we can expect, on average, for one of them to show significance when in fact there is actually no effect. To control for this problem, many scientists employ a Bonferroni correction, which simply means dividing the base significance level (0.05) by the number of tests conducted - in this case, apparently something greater than 200, although the true number is never stated by the authors. The appropriately conservative significance level for this paper would then be 0.00025.

The highest significance level for maternal consumption of alcohol in the paper was at <0.001 for "word-pair learning," and three of the other four significant tests were at 0.05. Perhaps, though, since first trimester alcohol consumption cropped up as a relatively high probability effect for five different learning and memory indexes (out of a total of 12, I think, but again it is not clear), it could be considered a real effect. But what other effects were real? The only effect that nearly every single time passes the Bonferroni level of significance was mother's IQ, which was significant at the 0.00001 level 5 times out of 6. So, even if there is a barely measurable effect on learning and memory on the children whose mothers drank, the IQ of their mother is 5000 times more important in determining that score. Also, for a given index, equally or more important than whether the mother drank was the child's current use of alcohol or tobacco. Race was more significant for four indexes. In two of the indexes, the child's gender was more significant.

The take-home message boils down to this. A lot of factors affect your children's mental abilities. Many of these are out of your control. The first trimester of pregnancy is certainly the most sensitive period for brain development. For a lot of women, morning sickness during that time means the last thing they are interested in is alcohol. Although these results are about as sketchy as you can get, it is certainly rational for women to abstain during the first timester, just in case. It took a lot of fishing for these authors to find a result they could publish, and they never discussed it in terms of relative importance to the other factors. Ironically, the mothers who seem to worry the most about alcohol during pregnancy are the high-powered, yuppie types with the big IQs to match - who it seems have the least to worry about. After all, their mothers went to cocktail parties while pregnant, and they still got into Ivy League schools.

So next time you see a visibly pregnant woman drinking a glass of wine in public (are there any of them left who have the guts to do it?), don't insist that it is your civic duty to give her a dressing down, because she is past the first trimester anyway. The stress you cause her is probably worse for her fetus than the wine.

Labels: health, humans, statistics