It didn't do anything to the Standard-American-Diet population in Chicago, IIRC -- I'll try to find the study.
They have hesitated to run with the "can't hurt might help" line of thinking after the bigger antioxidant trials started to come out. There's a plausible mechanism for action of antioxidants to prolong pregnancy, and while they were in trials everyone pretty much said, well goodness, vitamins C and E can't *hurt* you so go ahead and take them.
Then the study data showed that women supplementing antioxidants, while they didn't develop preeclampsia at higher rates, got sicker quicker, with earlier onset of preeclampsia and more severe cases.
And that made everyone say, wow. This is far more unintuitive than we thought. We had better stop saying, well it can't hurt, because we don't actually know.