No No No! Laxatives pass through the placenta and can be harmful!!
Your best bet (if you're constipated) is to drink a fiber drink like fibersure or metamucill or drink lots of water. You can even take a stool softener like Senekot if you are really bound up.
Avoid enemas too.
To whoever wrote that, Senekot is NOT a stool softener. It's a very powerful stimulant laxative. Do not take it while pregnant. Stool softeners include colace, Fibercon and other bulk forming fiber meds.