Take what your doc advises you to take, and make sure everything you're taking has been run past a doc. We used to say, hey, can't hurt, might help! a lot with this condition, but then it turned out that supplementing vitamins C and E (on the basis of a few very positive, but small, studies) was actually causing harm. Here's the Lancet abstract
, which says Concomitant supplementation with vitamin C and vitamin E does not prevent pre-eclampsia in women at risk, but does increase the rate of babies born with a low birthweight. As such, use of these high-dose antioxidants is not justified in pregnancy.
But the first initial studies looked very promising. This may also be the case with CoQ10, so I'd be very cautious indeed about taking it. Calcium does not change rate of preeclampsia
but does seem to lower overall maternal blood pressure in people eating Third-World quality diets; supplementation in a population in the US had no effect whatsoever. Dietary magnesium oxide supplementation has no benefit either. Here's a review
talking about dietary modifications and how they just don't work; in the calcium and baby aspirin cases this meta-analysis has been superceded by bigger randomized controlled trials, so ask your doc about those specifically.
I wish a dietary supplement would fix this, but incidence has been pretty steady worldwide and for a historical timeframe of about 2000 years, while diets and lifestyles have varied widely over that period and geographic distribution. Rates are going up in the US recently, mostly because of IVF and partly because it's heritable and more people are living through delivery these days.