I have b 12 deficiency and receive monthly injections. are there any concerns with trying to have a baby?

Unlikely: Given the fact that no animal reproduction studies have been conducted on cyanocobalamin, and that water-soluble vitamins cross the placenta, you should confirm this with your obstetrician. Most patients with B12 deficiency take 1000 mcg intramuscularly each month. This dosage may need to be elevated for pregnant women. I am unaware of any teratogenicity associated with vitamin b12, though.