I get what you're saying Kev but getting pregnant after the xmas album & before the sixth would be very much possible. She'll be 32 in April, as rivers pointed out, it only gets harder as the days tick by. I would say she would be willing to delay a sixth album for a baby. what's is another album compared to being a first time mom.
Brandon could easily switch to manage Kelly if she were to get pregnant & Narvel could look after Blake in the meantime. Or get someone else in their company temporarily.
But my bet is before July next year. Lets see if Im wrong