Cobalamin (Vitamin B12)

Vitamin B12 testing currently not a part of routine prenatal care, but may be included.  This nutrient is essential for red blood cell production, DNA synthesis, and fetal neurological development. Deficiency during pregnancy can lead to serious complications, including anemia and neural tube defects. This article covers the importance of B12 testing in pregnancy, reference ranges, and the most common causes of deficiency to help identify at-risk individuals.

Vitamin B12 Testing

The cobalamin (vitamin B12) test measures the amount of vitamin B12 in a serum sample. Vitamin B12 is also known as cobalamin because, structurally, it contains cobalt surrounded by a corrin ring structure.

Vitamin B12 is released from food by the actions of stomach acid and proteolytic enzymes in the mouth and stomach. Transcobalamin I is a haptocorrin protein produced by the salivary glands and stomach mucosa that binds to B12 to help stabilize it and facilitate absorption. It is synthesized via the TCN1 gene. In the stomach, B12 binds to a protein called intrinsic factor, which is produced in conjunction with hydrochloric acid. The complex protects B12 from degradation by stomach acids and facilitates absorption in the small intestines.

The absorption rate of B12 varies based on the amount of intrinsic factor produced and the binding capacity of intrinsic factor. Once in the bloodstream, transcobalamin I-bound vitamin B12 is transferred to transcobalamin II, and the complex binds to transcobalamin, a transport protein that delivers the vitamin to various tissues. TCN2 codes for the synthesis of transcobalamin II.

Once in the cells, vitamin B12 is converted to additional forms that include hydroxocobalamin, ​methylcobalamin and adenosylcobalamin. 

Cobalamin (vitamin B12) testing in pregnancy is not accurately reflective of cellular vitamin B12 status.

Vitamin B12 in Pregnancy

Serum vitamin B12 levels drop drastically throughout pregnancy as cellular need increases and there is increased hemodilution. During normal pregnancies, serum B12 levels drop 30% by the third trimester, yet dietary needs have increased twofold.

In the first few days postpartum, there is a sharp rise in serum vitamin B12 levels, as the hemodilution of pregnancy resolves. Levels return to normal pre-pregnancy levels by a few weeks postpartum.

High Vitamin B12 in Pregnancy

High maternal vitamin B12 (>600 pmol/L or 810 pg/mL) and folate have been associated with an increased risk for childhood autism.
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​This is an interesting correlation with no known etiology or mechanism of action yet. Other studies are in process regarding genetic variations and analysis of other biomarkers, as well as the link to unmetabolized folates.

Most Common Causes of High Vitamin B12 in Pregnancy

• Genetic Variants (TCN2, MTR, MTRR)
• Liver Disease
• Excess Supplementation
• Recent Supplementation
• Kidney Disease
• Smoking

Low Vitamin B12 in Pregnancy

Vitamin B12 deficiency has been associated with cognitive alternations in fetal brains, causing cognitive impairment that includes poor memory, language, and motor skills as well as preterm birth, anemia, and insulin resistance.

Most Common Causes of Low Vitamin B12 in Pregnancy

• Low Vitamin B12 Intake (Vegan Diets)
• Genetic Variants (TCN1)
• Hypochlorhydria
• Dysbiosis
• Inflammatory Bowel Disease (Ulcerative Colitis, Celiac Disease, Crohn's)
• Pancreatic Insufficiency
• Certain Medications (Proton Pump Inhibitors, H2 Antagonists)
• History of Bariatric Surgery

There is no “gold standard” for the diagnosis of vitamin B12 deficiency. Generally, diagnosis is determined via functional testing as well as serum B12 levels. These can include biomarkers found in the complete blood count (CBC), homocysteine, methylmalonic acid, and serum B12, in conjunction with symptomology.

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Medical Disclaimer:
This content is for educational purposes only and is intended for licensed medical professionals. It is based on current research, subject to change, and not intended to diagnose, treat, or prevent any medical condition. This information does not replace consultation with a qualified healthcare provider. Seek professional medical evaluation and treatment from a licensed provider. Use of this information is at your own risk.​

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