It is best to avoid this herb when you are pregnant and lactating. While there is not conclusive evidence as to negative affects, recent studies have suggested that it may be harmful both to the baby and the mother. It is thought that St. John's Wort may contribute to lower birth weights, as well as interact negatively with medications.
St Johns Wort should not affect your pregnancy at all, meaning it should be okay for you to take. You should check with your doctor first, though - also, the answer may be different if/when you start breastfeeding, so ask your doctor about that too.
I would reccomend you asking your doctor if the medication is safe to take while pregnant. I personally would not take anything that was not prescribed to me by a doctor while I was pregnant. Also just eat a healthy diet and you should have a happy and healthy pregnancy.
It is recommend that you do not take it during pregnancy, it could possibly cause premature labor. However speak to your doctor if you are taking it for depression.
You should check with your doctor before continuing the supplements while pregnant. Some may have harmful side effects and you want to be sure you are okay.