This can only be decided on an individual basis and preferably with advice from a perinatal psychiatrist taking into account your own personal history.
However, it is the case that many contemporary perinatal experts do not regard some medications, notably lithium, as being as harmful to the fetus as previously believed.
Thus many women have stayed well on their lithium while pregnant with no ill-effects to the baby. If medication is continued, it is important to monitor mother and baby closely.