Read this last night, whilst having my 1 glass of red wine for the evening to celebrate New Year.
Sorry, to me it really is just too simple to link drinking 4 units of alchohol a week in pregnancy to causing ADHD. 4 units really is very little and, depending on your build, alcohol tolerance levels, how quickly you quaff your drink etc it will not adversely affect a substantial proportion of pregnant women, at least imo.
I'm sticking to the current advice of one or two drinks once or twice a week, and I'm happy with that. Incidentally, followed that advice for dd1 and no, she doesn't have ADHD.