A new study and a review of studies out this month just killed the vitamin D idea. Or at least, they really ought to. I imagine there is still research in the pipeline, but I can't imagine there being a lot of new proposals after these:http://www.ncbi.nlm.nih.gov/pubmed/22336906There was no significant difference in the median serum vitamin D MoM or raw values within the outcome groups (P=141 and P=0.231, respectively) whereas the median PAPP-A MoM, uterine PI MoM and MAP MoM were significantly different (P=0.031, P=0.001 and P<0.0001, respectively)...
In other words, our D levels are average at the end of the first trimester. But other stuff is clearly already broken. So it's not causal.
andhttp://www.ncbi.nlm.nih.gov/pubmed/22336854Vitamin D supplementation in a single or continued dose during pregnancy increases serum vitamin D concentrations as measured by 25-hydroxyvitamin D at term.
In other words, *that's the only thing it seems to do*. It doesn't affect rate of onset of anything, it doesn't improve outcomes, but when you check the bloodwork, supplemented women have more vitamin D in the bloodstream.
No one would say this data completely rules out the possibility that supplementing vitamin D might help. But that doesn't mean that it is at all likely to help. It means, instead, that science can't prove a negative. If D were going to be a significant tool in our toolbox, we would see some differences in serum D levels in our population early and raising D levels would lower risk.
I'll probably write up a bit more on this for the main blog in a bit!