Managing hypertension in pregnancy is difficult in the sense that there is not a lot of data to guide us. Most of the drugs listed as "safe during pregnancy" are considered so largely based on many years of experience.
With that said, here are a list of medications which can be used, and those which should be avoided:
1st line agents: labetalol, hydralazine, alpha-methyl dopa, and calcium-channel blockers.
some possible side effects : beta-blockers (which are associated with low birth weight) and diuretics.
definitely contraindicated: ACE-inhibitors; ARBs. The classical teaching was that ACE-inhibitors were tolerable during the 1st trimester but needed to be avoided after that; more recent suggests that even 1st trimester ACE-I use is associated with an increased risk of fetal malformations.