In short, if you think that your occupation may pose a risk to a pregnancy, then a change in job, or working practice, may be necessary.

http://www.patient.co.uk/health/planning-to-become-pregnant

The above are just examples. In short, if you think that your occupation may pose a risk to a pregnancy, then you should discuss this with your employer before becoming pregnant. A change in job, or working practice, may be necessary.