I am married to an AH for 18 yrs. I can see how each new stressor and major responsibility caused an increase in drinking. Of course this makes sense since drinking is the coping mechanism. I remember when we had our 2nd daughter, the drinking increased to 4 a night. Now I think, 4 a night, what was I worried about? 15 yrs later he's up to 6-8/night.
I would worry that the increased stress of a child could trigger a relapse. Perhaps this is what he's trying to tell you. He may not be able to hendle the stress of a child.
The prospect of failure is much more acute in amy AH. Just the prospect of failure can cause increased drinking, negative thinking etc. If he's afraid he's going to fail as a father it can really do a number on his psyche that you can't fix.