As long as you can afford to give up your job early in your pregnancy then I'd say go ahead with it. If you hate your job now, you may hate it even more once you are pregnant. If like me, preggy brain hits you early you can find it very difficult to do your job well. I have a complex admin job and my brain is just not up to doing it properly at the moment and I'm getting further and further behind. I never realised how much your memory can be affected in pregnancy, I just thought it was an excuse pregnant women used, but let me tell you it's very real. I just wish I could walk away from all the stress, but as I have to go back to work after bubs is born (damn mortgage) I can't. If you can afford to walk away from it all if the going gets tough then by all means go ahead.

It might also be worth changing jobs first though. If like me it takes you many years to have a successful pregnancy (all the time thinking one's just around the corner for you) you could find yourself stuck in a job you don't like for a very long time, thinking it will only just be a few more months til you succeed.