It is safe to take during pregnancy. IT is often prescribed for women who may have had some spotting or for other reasons during the first trimester. (sometimes afterwards.) The efficacy is often debated, as some research shows that it may not work, but it does not HURT to take it. SO many docs do prescribe it.
I took it with my second as I had some major bleeding during my 16th week. I took the full round, bleeding stopped and I went to have a healthy baby.