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Folic acid and Vitamin B12 in pregnancy

Checked: 23-02-2021 by Rob Adams Next Review: 23-02-2022

Folic acid

Folic acid supplements at a dose of 400ug daily should ideally be taken pre-conceptually and then for the first 12 weeks of pregnancy.

If there is a higher risk of neural tube defects then a dose of 5mg daily should be recommended (1) for the first 12 weeks of pregnancy. Risk factors include:

Family history (maternal or paternal) of a neural tube defect
Previous pregnancy affected by a neural tube defect
Maternal diabetes
Maternal anti-epileptic drugs
Maternal coeliac disease
Maternal sickle cell anaemia
Maternal BMI >30

(1)CKS : Antenatal care - uncomplicated pregnancy

Additionally patients with the following conditions should also be advised to take 5mg daily throughout their pregnancy:

Patients with malabsorption following small bowel resection (2)
Patients on sulphasalazine (2)
Patients with haemoglobinopathies (including thalassaemia trait) (3)

(2)FSRH Clinical Guideline: SRH for Individuals with Inflammatory Bowel Disease (IBD), PDF Version (October 2016) - Faculty of Sexual and Reproductive Healthcare

(3)Scenario: Advice for all women | Management | Pre-conception - advice and management | CKS | NICE

Vitamin B12

Pregnant women already on vitamin B12 supplements

Although there are no published studies looking into congenital malformations following use of vitamin B₁₂during pregnancy, there is no evidence that treatment with vitamin B₁₂ is associated with an increased risk of congenital malformations or other adverse foetal effects due to in utero exposure.(1)

Vitamin B12 supplements in pregnancy

Vitamin B12 supplements are not routinely recommended in uncomplicated pregnancy.

Screening for Vitamin B12 deficiency in pregnancy

There is evidence to suggest that maternal vitamin B₁₂ deficiency increases the risk of neural tube defects in the newborn (1). However, screening for vitamin B12 deficiency before or during pregnancy is currently not routinely recommended.

If a woman who is pregnant or is planning pregnancy presents with symptoms of, or is at risk of vitamin B12 deficiency then consider measuring vitamin B12 levels. See CKS guidelines on vitamin B12 and folate deficiency for information on at risk groups.

Dr Amanda Clark (consultant haematologist at UHBW) advises the following:

It is really quite rare for women to have true B12 deficiency in pregnancy – the body stores B12 for a long time. Vitamin B12 can be falsely reduced in pregnancy and finding low levels can lead to women starting intramuscular B12 and never coming off it. Of note, COCP also causes a falsely reduced (usually borderline B12).

Consider testing in patient's with

Anaemia that is not iron deficiency
Significant macrocytosis – pregnancy causes macrocytosis so an MCV of up to 105 is normal unless accompanied by anaemia – of note thresholds for anaemia are lower in pregnancy.
Concerning neurological symptoms.

If levels are low, there are currently no national or local guidelines (1) on how to treat in pregnancy, so please discuss with local maternity team for individual advice if needed.

Vitamin B12 deficiency: treatment during pregnancy.

Resources

(1)CKS : Antenatal care - uncomplicated pregnancy

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