Ideally, do this before you become pregnant; or, if the pregnancy is unplanned, as soon as possible.

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

If in doubt about any medical condition that you have or treatment that you take with regard to their effect on pregnancy then see your doctor. Ideally, do this before you become pregnant; or, if the pregnancy is unplanned, as soon as possible.