Moderation in pregnancy is perhaps a more realistic and useful message.

Journalist Jill U. Adams aptly points to the lack of consensus and conflicting recommendations to pregnant women on their caffeine and alcohol consumption in her Los Angeles Times article "Pregnancy has room for a litle wine or beer, news studies show, but caffeine is a growing concern."

However, the article does not give a clear or useful message to pregnant women about the weight of scientific evidence concerning abstinence or moderation.

Ms. Adams' attempt to put the current studies into a broader context falls short. The article does little to interpret the studies' results in terms of prior findings and may muddy the water further by ending with a strong plug for abstinence in the case of alcohol - which contradicts the current study's findings - and no clear advice on caffeine. 

Two critical and easily understood points should be stated.

First, consuming high levels of alcohol ( 7 or more drinks per week) and caffeine (3 or more cups per day) are toxic to the fetus and a bad idea, period.

Second, at lower levels, the evidence for both is mixed and less certain. Direct relationships are difficult to evaluate in humans due to other factors that may also cause the outcome, in this case lower birth weight. These factors can include maternal nutrition, cultural factors (i.e. “normal” consumption patterns for the individual), maternal stress and the presence of other chemical pollutants.

In these type of studies, epidemiologists measure and statistically control for the personal habits and lifestyle traits that commingle with caffeine and alcohol use and could also cause lower birth weight. The LA Times article did not address which factors the researchers in either study controlled for.

Also missing was a key finding relating to caffeine metabolism, which is a personal factor that was not controlled in the study. Researchers found a clear and stark difference in how caffeine was associated with birthweight between women who were slow or fast metabolizers of caffeine.  Caffeine was not related to birthweight   among women with slow caffeine metabolism (caffeine circulated in the body longer) but was significantly associated with lower birthweight in babies born to the fast metabolizers. 

Is it possible that the relationship between caffeine and birthweight was clouded by individual differences in genetics, nutrition, stress and other chemical exposures? We can't tell because the primary results were not adjusted for differences in metabolism.

Great confusion lies in what to advise women during their pregnancy when epidemiology studies produce differing and sometimes contradictory results. Instead of waiting for the definitive study to give us specific limits of how much is safe, it may be more crucial to emphasize the importance of moderation in pregnancy and avoid undue stress or deprivation to a pregnant woman.

A woman's behaviors during pregnancy are extremely important in determining the health of the child. Pregnant women heed recommendations from their doctors and from the media, regardless of whether they are based on sound science.  Therefore, we should try extra hard as researchers and as reporters to provide the best information possible.

Moderation is known to prevent disease in non-pregnant people, and it probably works in pregnancy too.