Use of high doses is recommended only if clearly needed and the benefit outweighs the risk.

AU TGA pregnancy category: Exempt
US FDA pregnancy category: C

Comments:
-There is no data on intravenous use in pregnant women to know this drugs risks, including the risk of fetal harm or reproductive effects.
-The US recommended dietary allowance of vitamin B12 during pregnancy is 2.6 mcg.
-According to some authorities pregnant women who are vegans or lacto-ovo vegetarians should supplement B12 during pregnancy.
-Untreated B12 deficiency can lead to severe and permanent neurological damage in infants.

Animal studies of high dose administration (75, 150, and 300 mg/kg/day) during organogenesis showed maternal toxicity and fewer live births (due to increased resorptions). Animal studies at doses similar to high dose exposure (5 gram human dose) showed skeletal and soft tissue abnormalities (including incomplete skeletal ossification, rudimentary or small legs, flexed, rigid flexor or medially rotated limbs, domed heads, enlarged fontanels of the ventricles of the brain, bowed or large ribs, dilated ventricles of the brain, and thick wall of the stomach). Vitamin B12 readily crosses the placenta. There are no controlled data of high dose administration in human pregnancy.

AU Exempt: Medications exempted from pregnancy classification are not absolutely safe for use in pregnancy in all circumstances. Some exempted medicines, for example the complementary medicine, St John's Wort, may interact with other medicines and induce unexpected adverse effects in the mother and/or fetus.

US FDA pregnancy category C: Animal reproduction studies have shown an adverse effect on the fetus and there are no adequate and well-controlled studies in humans, but potential benefits may warrant use of the drug in pregnant women despite potential risks.

See references

Safety of high dose administration has not been established.

Excreted into human milk: Yes

Comments:
-Breastfeeding is not a contraindication for high doses when used for life-threatening situations, such as cyanide poisoning, however breastfeeding should cease after a high dose has been given because of the unknown potential for effects in the child.
-The recommended daily intake (RDI) of B12 for lactation is 2.8 mcg, and for infants under 6 months it is 0.4 mcg.
-Supplementation may be needed during lactation to achieve the RDI or correct a deficiency; doses of 50 to 100 mcg or more may be needed to correct deficiency during lactation (these doses do not expose the infant to excessive B12 and may improve status if B12 was previously inadequate).
-B12 deficiency in infants may cause anemia, abnormal skin and hair development, convulsions, failure to thrive, and delayed mental development.
-B12 levels are not reduced by flash heat pasteurization of breastmilk.

See references