Vitamin B12 in Pregnancy: Why It Matters for Mom and Baby

Vitamin B12, also called cobalamin, is a nutrient your body needs to make DNA and red blood cells.

It also helps keep your nerve cells healthy.

Your body cannot make vitamin B12 on its own.

You have to get it from food or supplements.

B12 is found almost only in animal foods.

• Meat, especially beef and liver
• Fish and shellfish, like salmon and clams
• Eggs
• Milk, cheese, and yogurt
• Fortified cereals and plant milks

During pregnancy, a mother's body needs extra vitamin B12.

The baby depends fully on the mother for this nutrient before birth.

After birth, the baby gets B12 through breast milk.

Low B12 in the mother can mean low B12 in her milk too.

Vitamin B12 deficiency in pregnancy is fairly common, especially in women who eat little or no animal food, such as vegans and some vegetarians.

It can also happen in women with digestive conditions that block B12 absorption.

Low B12 during pregnancy has long been linked to problems like anemia and nerve issues in the mother.

New research also points to effects on the baby's metabolism that were not well understood before.^[1]

A 2026 study in mice looked at what happens when mothers do not get enough vitamin B12 during pregnancy and nursing.^[1]

The mothers with low B12 had worse blood sugar control and worse reproductive outcomes.^[1]

Their pups also gained more weight later, especially when fed a high-fat diet.^[1]

The researchers traced this effect to the gut microbiome, the community of bacteria living in the gut.^[1]

Low maternal B12 reduced a specific gut bacterium called Bifidobacterium pseudolongum in both mothers and pups.^[1]

Bifidobacterium is a genus of bacteria often linked to gut health and is found in some probiotic foods and supplements.

The pups picked up less of this bacterium during the newborn nursing period, which seemed to be a key window of time.^[1]

Giving the pups back this bacterium, or its byproduct acetate, reduced the extra weight gain.^[1]

Acetate is a short chain fatty acid made by gut bacteria when they digest fiber.

In this study, acetate worked through a receptor called Ffar2 to turn up a gene called Ehhadh, which is involved in how the body burns fat.^[1]

This is animal research, so it cannot directly prove the same chain of events happens in people.

Still, it adds to a growing picture that a mother's diet can shape her baby's gut bacteria and metabolism long after birth.

Vitamin B12 works closely with folate, another B vitamin, to help make DNA.

This partnership is one reason both nutrients are stressed so much in pregnancy.

B12 also helps make myelin, the protective coating around nerves.

Without enough B12, nerve signals can slow down or become damaged over time.

B12 helps break down homocysteine, an amino acid in the blood.

High homocysteine has been linked to heart and blood vessel problems.

Low B12 can also cause a type of anemia called megaloblastic anemia, where red blood cells are too large and do not work well.

• People who eat vegan or strict vegetarian diets
• Older adults, since the stomach absorbs B12 less well with age
• People with conditions like celiac disease or Crohn's disease
• People who have had weight loss surgery
• People taking long term acid reflux medication or metformin
• Pregnant and breastfeeding women, due to higher needs

• Ongoing tiredness or weakness
• Pale or yellowish skin
• Tingling or numbness in hands and feet
• Trouble with balance
• Memory problems or brain fog
• Sore tongue or mouth ulcers

These signs can build up slowly, sometimes over years, since the body stores some B12 in the liver.

Most people who eat meat, fish, eggs, or dairy regularly get enough vitamin B12 from food.

A few simple habits can help protect your B12 status, especially during pregnancy and breastfeeding.

• Include an animal protein source, like eggs, fish, or dairy, in meals most days if your diet allows it
• Choose fortified foods, like fortified cereal or plant milk, if you eat little or no animal food
• Talk with a doctor about checking your B12 level before or during pregnancy if you follow a vegan or vegetarian diet
• Ask about testing if you take metformin or long term acid reducing medication
• Mention any tingling, numbness, or unusual tiredness to a healthcare provider
• Discuss any supplement use with a doctor rather than starting on your own, since needs vary by person

The mouse study raises interesting questions about probiotics and infant gut health.^[1]

Bifidobacterium species are already among the most common bacteria in the gut of breastfed babies.

Human milk contains special sugars that feed these bacteria and help them grow.

Researchers are still working out how much maternal nutrition, including B12, actually shapes this process in humans.^[1]

For now, the clearest, evidence backed step for mothers is simply getting enough vitamin B12 from food or, when advised by a doctor, from supplements.