Congratulations on your baby!! I'm glad to hear someone trying this when they're pregnant. Seems like a time you would need it most, being that when I have most of my gall bladder problems!
I don't know why it took me so long to make the connection from mag sulfate to manesium sulfate. I was put on mag(magnesium) sulfate twice when I was pregnant with my first child to stop labor. It successfully stopped the labor. But my experience from having intravenously in the hopsital to ingesting it orally has been very different.
I don't think I have ever been more miserable than when I had mag sulfate intravenously. I was a noodle for 24 hours. No muscle tone at all. Granted, it has been 7 years, but the 2 experiences are hard to forget. I remember it being very difficult to go to the bathroom afterward. It was days until I had a BM. Which is very much unlike my experience taking magnesium sulfate orally. Perhaps this difference is why they don't recommend taking it while pregnant? (Not that I am any way agreeing with anything Suga has said!)
I don't know whether it's good or not while you're pregnant. I just wanted to let you know my experience with it to stop my labor. I think as with anything it is crucial to trust your body and what your instincts tell you. We're the only ones who can know what's best for our bodies!