I refer to my hoped for second child as potential number 2, but I too loathe 4-oh and bubba/babba. In fact my PILs still refer to my OH as babba, so as soon as they started also calling my bump it I pointed out that that reminds me of an evil witch (well, Baba Yaga, close enough) and would they please stop, which gave them pause... and they stopped /that/ nickname at least.