On the one hand, okay, about the only thing we know about the sprout just now is what bits he's got. But on the other hand, does it really matter to me in the slightest that this baby has boy bits? Would I welcome him differently if he had girl bits? I'd probably be less careful of changing his diaper, but as he lives in DC and I live in Minnesota, this is unlikely to be an issue. And otherwise no. It tells me nothing about his future personality, about what he can expect from life or what he'll come to want. So what would be wrong with a card saying, "Welcome, little one"?
I know, crunchy hippie freaks who think things like that aren't supposed to buy Hallmark cards in the first place. Sigh.