Crack Babies

The NYT calls it "The Epidemic that Wasn't"

Eating Cereal Causes Boys?

The Wall Street Journal explains why observational studies can lead to misleading conclusions.
... But when it comes to human pregnancy, most of the time, observational studies are all there are. We all know clinical studies are better, but it's not ethical to use human pregnant woman and infants to study anything risky, like the safety of medications. So researchers have to basically follow what pregnant women do and then see what happens later, or study babies with health problems and try to figure out what their parents might have done.
That's better than no research at all, but it can lead to a lot of misguided conclusions.