Sorry, I know one person said to ask a trainer and not a doctor -- but the trainer doesn't know about the anatomy of a pregnant woman like a doctor would. I would not want to put my pregnancy's success in the hands of a trainer, however great he or she was. I'd ask my obstetrician and mine, at least, wouldn't refer me back to a trainer; she'd check the literature and ask other doctors and give me an informed answer. (But I have a pretty great doctor.) Not all doctors automatically default to either "Ask a trainer" or "Don't ever do anything ever again while pregnant."
There are many kinds of exercise, including pretty vigorous ones, you can do while pregnant; why take the risk of doing any exercise that could create problems? Do some research on other forms of exercise too. If you can't kickbox, well, you will get back to kickboxing in less than 9 months anyway.