Dimple - my phd was in developmental genetics and yes, it really is that coordinated a process! It's quite mind blowing to watch an embryo form from a single cell under the microscope - each stage, in some species hour by hour, is catalogued and known.
Obviously we can't go around splashing ethanol on human foetuses and seeing what happens, so we take the very broad view, which is that the critical process of 'turning a single cell into a complex structure with all the bits in the right place' happens in trimester one. And we say avoid alcohol then.
I've not drunk at all in pregnancy, but if I'm honest I would have had the odd glass at weddings/ weak beer with food if it didn't trigger my nausea.
We are targeting the wrong women- no one is going to be harmed by a whiff of prosecco over lunch, but there are still plenty of women drinking /smoking heavily / doing drugs- we need to target help and resources at them. That means more funding is needed, which is probably harder to do than putting the frighteners on ms. One tiny glass with lunch once a week.