I had mag sulfate with my DD at 34 weeks, and probably would not do it again. If I had known more then, I might not have done it then, either. We were "transfers", after planning a birth center birth (one staffed by cnms, where you get whatever cnm happens to be around). As it turned out, the cnm that showed up was the ONE we'd met and didn't like, and between her and the back-up OB, they were basically useless. According to the OB, at 34 weeks, you're right on the line of trying to decide do they or don't they try to stop the labor. Since I was 34 wks exactly, we decided to try. However, I'm pretty convinced that I had placental abruption, and I think they should have known, based on the amount of bleeding I had, and in retrospect, trying to stop labor could have been very risky to both my DD and I. The OB claims he couldn't see one on the u/s, but I don't believe he knew at all what he was doing with the thing, since he kept messing around with it trying to get measurements of DD, and then eventually gave up, and said she'd be around 3.5lbs (She was 5lbs, 10 oz). And a small abruption might not have been able to be seen, but IMO, given the amount of bleeding, they shouldn't have dismissed it as quickly as they did. In the end, when DD was born, her placenta came out immediately behind her feet. Luckily for both of us, the mag didn't work (though it did make me feel like crap), and we were still able to have a relatively natural birth. This time we're doing a lot of things differently.