Anemia. Folic acid, AKA folate (folic acid) (vit B9), is recommended for all women wanting to get pregnant -- 0.4mg (400mcg) daily, which is important for preventing birth defects like spina bifida. Women w/ a hx these disorders should take 10x that amt daily -- 4mg (4000mcg) through the 3rd month of pregnancy. It won't affect fertility, chances of conception/twins, or periods. Can help with anemia.
Because. It is essential to life as all the other vitamins are. Vita comes from the latin "vita" meaning life and "amin" was originally "amine" when vitamin b1 was first thought to be a chemical known as an amine. When it was found not to be an amine the e was dropped.