Actually it's one of the safest of all the nutrients. A European Commission study to identify the upper limit for vitamin supplements found an upper limit for every other Vitamin but declared that B12 is safe at any level. It's safe in your diet, it's safe when taken as a supplement, and it's safe hen recorded in the blood.
This is the important question. As you kno, with most supplements, you need permission to take them during pregnancy or when nursing.
By all means ask your doctor, midwife or health visitor, but the answer is YES.
B12 is vital for the healthy development of a baby, just as it was important to maintaining the hormone cycles and uterus repair that allowed you to get pregnant in the first place. B12 is vital for development of the nervous tissue, which happens in the first trimester of pregnancy, and for the ongoing development of the baby throughout pregnancy.
It's also valuable for your own well-being as a mother. The typical tendency of mammalian mothers is to give the baby what it needs at great cost to the mother, so if there isn't enough B12 to go around then the mother will typically suffer from a shortage (the baby may also suffer if there isn't enough for a rapidly growing baby). People we've put on to B12 replacement therapy during pregnancy have reported less morning sickness, much less nausea, more energy, and no post-natal depression. But before you get depressed that you didn't start earlier, it's never too late.
It's difficult to be sure what's due to B12 deficiency and what's due to something else, but babies from the same mother have been:
The definitive and original guide to B12 deficiency, Dr Chandy interviewed by Chris Jackson of UK BBC Inside Out Team broadcast 31 Oct 2008.
Dr Joseph Chandy explains symptoms and shows the restorative effect on one patient (other patients' families have asked that we edit out their stories unfortunately)
Dr Chandy was nominated for the North East Local Heroes award. The interviewer was at first surprised - people don't get awards for doing what they are paid to do - but she persisted.
Julia found her eyesight going as her eyes refused to focus on the same things as each other. She's been for all sorts of tests and treatment, but now that she's on B12 replacement therapy she's starting to see an improvement.
June describes her suffering when doctors didn't follow the standard protocol after any stomach or intestinal operation - to offer B12 replacement therapy
Susan gets very tired, which isn't much fun especially as she has so much to do. Here she tells her story.
Donna, like so many women, wants to live a normal life. Vitamin B12 could give her that chance.
New documentary out from Elissa Leonard in North America, featuring Sally Pacholok and many other internationally renowned experts.
Janette first appeared in the BBC InsideOut documentary in October 2006. Since then the NHS has forced her doctor to withdraw B12 replacement therapy on a number of occasions, and she tells of her struggles with having B12 and then having it taken away.
She has bravely agreed to be filmed without her usual wig, but her memory is playing up because it is so long since her last injection.
Frankie tells of how she suffered, the tests she had to endure until doctors worked out what was wrong, and what a difference it has made.
The Scottish Parliament discusses Pernicious Anaemia and vitamin B12 deficiency on Wednesday 7 March 2012.
This video is over 1 hour long and represents real political change - we are at last on our way.