The fact is, there is no necessity for any one of us ever having been called into existence at all anyway - even within wedlock, so our creation is not dependent upon either the sins or the sanctity of the parents. Certainly in both cases there are times when a child is conceived as well as not.
God creates whom He will as He wills - no one knows His will in that respect. All we know is that He always brings every single one of us into existence for His greater glory and for our own salvation.