The first suggestion I have (and I've been self-employed for years!) is to work up until the time you give birth, if you feel up to it. If you must take time out, that will cost you a lot of money, for sure, and your absence could have a negative impact on your business. While most women start maternity before their baby is born, as a business owner you might prefer to take all your time off after the birth of your baby if you are feeling well, and are having a healthy pregnancy, of course. Depending on the type of business you own, you could do most of your work at home after you give birth, or take your baby to work with you. Newborns sleep so much that they are unlikely to form a real distraction at work.
Did you notice that Italian Member of the European Parliament Licia Ronzulli recently took her baby to a session of the European Parliament, wearing it in a wrap? If she can do it, so can you! If you have decided that you don't want to work while in the final stages of your pregnancy, and while you have a newborn, it is best to interview replacements as early as possible in your pregnancy. If you can afford it, have your planned replacement working alongside you for a few months before you start maternity leave so that you get to know the person and can rest assured that your business is safe in their hands. For those of you who are employed, you might want to look at our article about when to tell your employer you are pregnant. For more interesting workplace stuff, see Australian sacked for being pregnant?