None of Your Business

This mother's day we spent some time with family. I got so annoyed with Rob's extended family--I got asked four times if I was pregnant. Just for the record I am not. But even if I was that's not something you ask. I felt like my personal boundaries were being repeatedly violated. I believe the conceiving of babies is a very personal thing--between husband and wife (and God). When we're ready to share our joy we'll tell you, until then its a taboo question. What made the whole thing even worse was that no one asked my sister-in-law if she was pregnant. I think I was even referred to as "the baby maker in the family"; what the hey? I have one child.
How do you tactfully deal with this situation?