"Speculation into the future"- Pregnancy and low levels of alcohol ingestion
This concerns the effects of low levels of alcohol on pregnancy. This issue actually cannot advance easily because experimental testing of this issue is unethical. Furthermore, additional epidemiology studies cannot be reliably done to provide useful further information. The older epidemiology data would need to be reexamined and reevaluated.
The reason for this is the following. Now that it is popularly thought that drinking even low levels of alcohol is adverse to the fetus, only individuals prone to participating in other high risk behaviors are likely to drink even low dose alcohol. Hence, the only epidemiologic evidence that can be reliably reviewed is the old data.
An epidemiology study usually provides the basis for creating a more definitive randomized clinical trial to determine if the effects seen in the epidemiologic study are simply associations or if they are rather truly causative. A clinical trial prospectively randomizing pregnant women to low dose alcohol versus no alcohol, which would answer this question, is not appropriate or ethical. Hence, this issue cannot progress in the typical fashion.
Epidemiology studies, even when well done, can lead to erroneous conclusions. (Examples of this include the prior epidemiology studies suggesting that female replacement hormones reduced cardiovascular disease only to have subsequent large randomized trials show this to be incorrect for the female replacement hormones most commonly in use.)
Medical science, when limited to epidemiology studies without follow up randomized experimental trials, becomes like the descriptive sciences of economics and sociology. Careful observations can be made, but the validity of the conclusions cannot subsequently be easily tested for accuracy.