Hi Julie! I'm a certified Healthy MOMs perinatal fitness instructor, group fitness instructor and personal trainer. Kickboxing is definitely NOT recommended during pregnancy due to the rapid directional changes that are involved that make you susceptible to injury were you to fall (due to change in center of gravity) and the relaxin in your joints that make them soft and, therefore, less protected.
On a funny note, I am training an OB/GYN here from Northwestern Memorial Hospital who also loves kickboxing and had to tell her to "knock" it off. I'd recommend finding another activity to do for these few short months so that post-partum you can continue to kickbox your way well into the future!!
jeni - momma to Olivia Rose (9/14/02) and due 7/20/05