I haven't started taking a pre-natal yet, though I've been taking 800 mcg Folic Acid, Calcium and Magnesium since a few months before we started TTC.
I am a carrier for a genetic trait (beta Thalassemia) that makes my red blood cells about 60% of normal size. If I take iron, it just taxes my liver as there is nowhere for it to go (tiny red blood cells already full.) When I'm at my maximum level of iron, I am borderline anemic compared to a normal woman.
During pg, I was advised to take iron, however, because I need to keep my iron as high as possible, plus the fetus might not carry the trait and s/he could possibly use more than I could. So now that I've had a BFP, I will start taking prenatals again soon. I got mine (a kosher brand) from my doctor last time.
I'm eating a serving of hemp seeds every day for the Omegas. I guess hemp seed/oil is the most perfect balance in nature of Omega-3 to Omega-6 for human needs. I feel better eating a food than taking a capsule, too, I guess.
I know I read something somewhere that was against flax seed oil in pregnancy, but that may have been one study, and I know I've heard people contest it elsewhere. Personally, I strongly prefer flax seed oil to fish oil, but I'm generally grossed out by fish.
--willo