Is taking vitamin d safe if your pregnant and which is better 400unit or 1000?

Both are fine: You are fine with either daily dose of vitamin d. Some studies have shown a decreased risk of preeclamapsia in women who take more vitamin d daily. For that reason, you may wish to opt for the 1000 iu.

Yes: Yes, vitamin d is safe during pregnancy, and is in fact often recommended during pregnancy, as low levels can potentially be harmful. The proper dose depends on you, and is something that should be discussed with your doctor.