Because of all the hormone changes, your skin in the down town maybe a little bit more sensitive than the usual, and might cause it to be more painful than the usual. I've got mummy friends who still went for waxing still although I personally didn't.
If it helps, you can read up on this article about the general does and don'ts during pregnancy.
http://sg.theasianparent.com/to-the-modern-woman-dont-try-this-while-pregnant/