Use of vitamin B12 in pregnancy

(Date: December 2017. Version: 2)

This factsheet has been written for members of the public by the UK Teratology Information Service (UKTIS). UKTIS is a not-for-profit organisation funded by the UK Health Security Agency (UKHSA) on behalf of UK Health Departments. UKTIS has been providing scientific information to health care providers since 1983 on the effects that medicines, recreational drugs and chemicals may have on the developing baby during pregnancy.

What is it?

Vitamin B12 (hydroxocobalamin, cyanocobalamin) occurs naturally in eggs, meat and dairy-based food, and is also present in certain vitamin supplements including some designed for use in pregnancy.

Deficiency of vitamin B12 can lead to anaemia (where oxygen-carrying red blood cells do not function correctly) and symptoms including extreme tiredness, weakness, mouth ulcers, pins and needles, and eyesight, psychological, and memory problems. If vitamin B12 deficiency is not treated, some of these problems can become permanent. Deficiency is diagnosed using blood tests and is usually treated with vitamin B12 injections, followed by tablets.

Large doses of vitamin B12 are occasionally used to treat people with cyanide poisoning which most frequently occurs following smoke inhalation after building fires. High dose vitamin B12 is also used to treat a rare genetic disorder called methylmalonic acidemia.

Is it safe to use vitamin B12 in pregnancy?

There is no strong evidence that women with a varied diet need to take a vitamin B12 supplement in pregnancy. However, there is no suggestion that taking a vitamin B12 supplement in pregnancy at the recommended dose harms the developing baby.
Numerous studies have suggested that vitamin B12 deficiency in pregnancy may be linked to a higher chance of neural tube defects (such as spina bifida) in the baby. Women who are pregnant or trying to conceive and are diagnosed with vitamin B12 deficiency should therefore receive vitamin B12 supplementation as recommended by their doctor.

Where treatment with high dose vitamin B12 is required as an antidote to cyanide following smoke inhalation, it should not be withheld because of pregnancy. The effects of cyanide poisoning are likely to cause far more harm to a pregnant woman and her baby than any possible adverse effects of treatment with high dose vitamin B12.

What if I have already taken vitamin B12 during pregnancy?

If you are pregnant and have taken any medicines it is always a good idea to let your doctor know in case you need any additional monitoring or treatment.

This leaflet summarises the scientific studies relating to the effects of vitamin B12 supplementation on a baby in the womb.

Can use of vitamin B12 in pregnancy cause my baby to be born with birth defects?

A baby’s body and most internal organs are formed during the first 12 weeks of pregnancy. It is mainly during this time that some medicines are known to cause birth defects.

No studies have investigated the chance of birth defects in babies born to women taking vitamin B12 at any dose in pregnancy. However, there are 17 case reports of babies without birth defects born to women taking high dose vitamin B12 to treat methylmalonic acidemia in pregnancy. While this is reassuring, large, well-designed studies of pregnancy outcomes in women taking vitamin B12 in pregnancy are ideally required.

Can use of vitamin B12 in pregnancy cause miscarriage or stillbirth?

No studies have investigated the likelihood of miscarriage or stillbirth in women taking vitamin B12 at any dose in pregnancy. Research into this subject is therefore required.

Can use of vitamin B12 in pregnancy cause preterm birth or my baby to be small at birth (low birth weight)?

No studies have assessed the chance of preterm birth or low infant birth weight following use of vitamin B12 at any dose in pregnancy. Research into this subject is therefore required.

Can taking vitamin B12 in pregnancy cause learning or behavioural problems in the child?

A baby’s brain continues to develop right up until the end of pregnancy. It is therefore possible that taking certain medicines at any stage of pregnancy could have a lasting effect on a child’s learning or behaviour.

No studies have investigated learning and development in children exposed to vitamin B12 in the womb. Research into this subject is therefore required.

Will my baby need extra monitoring during pregnancy?

As part of their routine antenatal care, most women will be offered a scan at around 20 weeks of pregnancy to look for birth defects and to check the baby’s growth.

Use of a vitamin B12 supplement in pregnancy is not expected to cause any problems that require additional monitoring of the baby. Women diagnosed with a vitamin B12 deficiency in early pregnancy may receive more detailed anomaly scans to check for neural tube defects in the baby.

Pregnant women who have received treatment with high dose vitamin B12 following smoke inhalation, or to treat the genetic disorder methylmalonic acidemia, are likely to receive additional monitoring to ensure that these issues have not affected their baby’s growth and development.

Are there any risks to my baby if the father has taken vitamin B12?

We would not expect any increased risk to your baby if the father used vitamin B12 before or around the time you became pregnant.

Who can I talk to if I have questions?

If you have any questions regarding the information in this leaflet please discuss them with your healthcare provider. They can access more detailed medical and scientific information from

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General information 

Up to 1 out of every 5 pregnancies ends in a miscarriage, and 1 in 40 babies are born with a birth defect. These are referred to as the background population risks.  They describe the chance of these events happening for any pregnancy before taking factors such as the mother’s health during pregnancy, her lifestyle, medicines she takes and the genetic make up of her and the baby’s father into account.

Medicines use in pregnancy

Most medicines used by the mother will cross the placenta and reach the baby. Sometimes this may have beneficial effects for the baby.  There are, however, some medicines that can harm a baby’s normal development.  How a medicine affects a baby may depend on the stage of pregnancy when the medicine is taken. If you are on regular medication you should discuss these effects with your doctor/health care team before becoming pregnant.

If a new medicine is suggested for you during pregnancy, please ensure the doctor or health care professional treating you is aware of your pregnancy.

When deciding whether or not to use a medicine in pregnancy you need to weigh up how the medicine might improve your and/or your unborn baby’s health against any possible problems that the drug may cause. Our bumps leaflets are written to provide you with a summary of what is known about use of a specific medicine in pregnancy so that you can decide together with your health care provider what is best for you and your baby.   

Every pregnancy is unique. The decision to start, stop, continue or change a prescribed medicine before or during pregnancy should be made in consultation with your health care provider. It is very helpful if you can record all your medication taken in pregnancy in your hand held maternity records.

Disclaimer: This information is not intended to replace the individual care and advice of your health care provider. New information is continually becoming available. Whilst every effort will be made to ensure that this information is accurate and up to date at the time of publication, we cannot cover every eventuality and the information providers cannot be held responsible for any adverse outcomes following decisions made on the basis of this information. We strongly advise that printouts should NOT be kept for any length of time, or for “future reference” as they can rapidly become out of date.

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