How do folate, (folic acid) vitamin b12 and iron help in pregnancy for mom and baby?

Healthy mom, baby: Developing fetus will get the nutrients it needs from mom. It gets calcium from mom's blood (via mom's diet, or her bones-doesn't care). Need B12 and folate (folic acid) for normal neurological development, to prevent some congenital abn; needs iron for cell growth and development. Mom needs supplement to prevent deficiencies (increased needs due to fetal development).

Several benefits: Folate (folic acid) cuts back on fetal spina bifida risk, possibly heart defect, and, in some genetically susceptible people, can improve homosistein levels and coagulation errors.