Given a choice I would rather come out to everyone at once, then do a death by a thousand cuts, telling people one by one. I wish I would have rented a hall and given everyone the same power-point and then left telling them all to discuss it amongst themselves.
That being said, I think that its so case specific, in that every set of parents reacts in different manner, so its hard to give general advice other than tell the truth. Yeah, its always a last resort I know, but in this matter it tends to work out better than all the science and all the explanations, most of which do not explain, but merely excuse.