During pregnancy it is extremely important that you don't let yourself become constipated. If you are going to embark on a serious colon cleansing program I would suggest that you do it now beforehand, and not while you are pregnant.
Once you become pregnant, gentle saline solution cleansing enemas using an enema bag can safely be used as required to maintain regularity and a clean colon.
Information on taking a comfortable and effective enema can be found at the following links: