FWIW, here’s a Cochrane review on RCTs of such encouragement designs. It’s basically a failed meta-analysis in that the data is too spotty to make any conclusions. But it shows at the very least that such studies have been done before. An encouragement design in a population with high alcohol use seems most promising for figuring out the causal effect on fetuses, as you say.
(Another recent meta-analysis on the same question finds a slight decrease in preterm birth in the alcohol education group, but this is based on just three studies and marginally significant so I’d say it’s still uncertain.)
Good question—my reasoning was that homicide is well-measured and easy to find online, and should correlate with levels of crime more broadly. I wonder what variable we would want to address the Thailand issue...maybe the share of prisoners who are “violent” would be useful, but I’d be surprised if I could find it for many countries.