Magnesium is an essential mineral that supports over 300 bodily functions, including muscle and nerve activity, blood glucose regulation, and bone development. During pregnancy, adequate magnesium intake is important for both maternal wellbeing and foetal growth. Whilst most pregnant women can obtain sufficient magnesium through a balanced diet rich in green leafy vegetables, nuts, seeds, and whole grains, some may require supplementation. The NHS advises that taking 400 mg or less daily of supplemental magnesium is unlikely to cause harm. However, it is essential to consult your midwife or GP before starting any magnesium supplement during pregnancy to ensure it is appropriate for your individual circumstances.

Can I Take Magnesium While Pregnant?

Yes, magnesium is generally safe to take during pregnancy when used appropriately, and it plays an important role in both maternal and foetal health. Magnesium is an essential mineral involved in over 300 enzymatic reactions in the body, including muscle and nerve function, blood glucose control, and bone development.

Most pregnant women can obtain adequate magnesium through a balanced diet rich in green leafy vegetables, nuts, seeds, whole grains, and legumes. The UK reference nutrient intake (RNI) for adult women, including during pregnancy, is 270 mg per day. Routine magnesium supplementation is not recommended for all pregnant women unless there is a clinical indication.

According to NHS guidance, taking 400 mg or less a day of supplemental magnesium is unlikely to cause harm. However, it is essential to consult your midwife or GP before starting any magnesium supplement during pregnancy. Whilst magnesium is generally well-tolerated, excessive intake can cause adverse effects, and certain medical conditions or medications may interact with magnesium supplementation.

Your healthcare provider can assess your individual needs, review your dietary intake, and determine whether supplementation is appropriate for your circumstances. Self-prescribing supplements without medical advice is not recommended, as individualised care is crucial for optimal maternal and foetal outcomes.

Benefits of Magnesium During Pregnancy

Magnesium provides several potential benefits during pregnancy, supporting both maternal wellbeing and foetal development. In hospital settings, magnesium sulphate is used for seizure prophylaxis in severe pre-eclampsia and eclampsia, a serious condition characterised by high blood pressure and protein in the urine. It's important to note that oral magnesium supplements are not recommended by NICE for pre-eclampsia prevention.

Magnesium may help with common pregnancy discomforts, particularly leg cramps that many women experience. However, evidence for magnesium supplementation to relieve pregnancy-related leg cramps is mixed, and non-pharmacological measures such as stretching exercises are often recommended first. The mineral's role in muscle relaxation and nerve transmission may provide some relief from these uncomfortable symptoms.

For foetal development, magnesium contributes to building bones and teeth, as it works alongside calcium and vitamin D in skeletal formation. The mineral also supports the development of the baby's nervous system.

Magnesium sulphate is used in hospital settings when preterm birth is imminent, not to delay labour but for foetal neuroprotection, helping to protect the baby's developing brain. This is administered intravenously by healthcare professionals and is different from oral magnesium supplements.

While some research suggests magnesium may have benefits for sleep quality, anxiety reduction, and glucose metabolism during pregnancy, evidence for these effects is limited. Your healthcare provider can advise whether magnesium might be helpful for your specific circumstances based on current evidence and your individual health needs.

Safe Magnesium Dosage for Pregnant Women

The recommended daily intake of magnesium for adult women, including during pregnancy, is 270 mg per day according to UK reference nutrient intake (RNI) guidelines. For adolescent girls (aged 15-18) who are pregnant, the RNI is typically around 300 mg daily to support their own continued growth alongside foetal development.

Many women can meet their magnesium needs through a well-balanced diet without requiring supplementation. Foods rich in magnesium include spinach, chard, pumpkin seeds, almonds, black beans, avocado, dark chocolate, whole grains, and fatty fish such as mackerel. A varied diet incorporating these foods can provide adequate magnesium for most pregnant women.

When supplementation is necessary, the NHS advises that taking 400 mg or less a day of supplemental magnesium is unlikely to cause harm. This refers to elemental magnesium from supplements, not including dietary sources. It's important to count the total magnesium from all supplements you take, including prenatal vitamins, as many contain magnesium.

Timing of supplementation can affect absorption and tolerability. Taking magnesium with food generally improves absorption and reduces gastrointestinal side effects. If you're also taking iron supplements or certain antibiotics, separate these from magnesium by at least 2 hours. For levothyroxine, maintain at least a 4-hour gap between taking it and magnesium supplements.

Some women find that splitting the dose throughout the day, rather than taking it all at once, minimises digestive discomfort. Your midwife or GP can provide personalised guidance on the appropriate dosage, timing, and duration of supplementation based on your medical history and current symptoms.

Types of Magnesium Supplements in Pregnancy

Several forms of magnesium supplements are available, each with different absorption rates, bioavailability, and potential side effects. Understanding these differences helps ensure you choose the most appropriate supplement for your needs during pregnancy.

Magnesium oxide is one of the most common and affordable forms, containing a high percentage of elemental magnesium. However, it has relatively poor bioavailability, meaning less is absorbed by the body. This form is more likely to cause digestive side effects, particularly loose stools, which can actually be beneficial for pregnant women experiencing constipation.

Magnesium citrate offers better absorption than magnesium oxide and is generally well-tolerated. It combines magnesium with citric acid and is often recommended for pregnant women due to its good bioavailability and effectiveness. This form may have a mild laxative effect, which can help with pregnancy-related constipation.

Magnesium glycinate (or bisglycinate) is bound to the amino acid glycine, resulting in excellent absorption and minimal gastrointestinal side effects. This form is particularly suitable for pregnant women who experience digestive sensitivity.

Other forms include magnesium malate and magnesium threonate, though research on their specific benefits during pregnancy is limited.

When taking magnesium alongside other minerals, be aware that high doses of calcium or iron taken simultaneously can compete with magnesium for absorption. If you take multiple supplements, it may be better to space them throughout the day.

Most magnesium supplements are classified as food supplements rather than medicines. Choose reputable UK brands with clear labelling and evidence of quality control. If you're considering a licensed magnesium medicine, look for a UK product licence (PL) number on the packaging. Always check that any supplement you consider is suitable for use during pregnancy.

When to Avoid Magnesium During Pregnancy

Whilst magnesium supplementation is generally safe during pregnancy, certain medical conditions and circumstances require caution or complete avoidance. Women with kidney disease or impaired renal function should not take magnesium supplements without specialist supervision, as the kidneys are responsible for excreting excess magnesium. Reduced kidney function can lead to dangerous accumulation of magnesium in the blood (hypermagnesaemia), which can cause serious complications including cardiac arrhythmias and respiratory depression.

Myasthenia gravis, a neuromuscular condition, is a contraindication for magnesium supplementation, as magnesium can worsen muscle weakness and interfere with neuromuscular transmission. Women with this condition should discuss alternative approaches with their neurologist and obstetrician.

Certain medications interact with magnesium supplements, potentially reducing their effectiveness or causing adverse effects. These include:

• Iron supplements – separate from magnesium by at least 2 hours

• Levothyroxine – take at least 4 hours apart from magnesium

• Antibiotics (particularly tetracyclines and quinolones) – separate by at least 2 hours

• Bisphosphonates (for bone health) – magnesium can reduce their absorption

• Diuretics – some increase magnesium loss, whilst others (potassium-sparing diuretics) may cause magnesium retention

• Proton pump inhibitors – long-term use may affect magnesium levels

• Muscle relaxants – magnesium may enhance their effects

Be aware that some antacids and laxatives contain magnesium. Check labels carefully to avoid inadvertently exceeding safe levels when taking multiple products.

Signs of excessive magnesium intake include persistent diarrhoea, nausea, abdominal cramping, lethargy, and in severe cases, irregular heartbeat, difficulty breathing, or confusion. If you experience any of these symptoms whilst taking magnesium supplements, stop taking them immediately and contact your healthcare provider. Seek urgent medical help for severe symptoms such as breathing difficulties, marked weakness, or collapse.

Women with heart block or other cardiac conduction disorders should use magnesium supplements only under medical supervision.

Speaking to Your Midwife or GP About Magnesium

Open communication with your healthcare team is essential before starting any supplement during pregnancy, including magnesium. Your midwife or GP can provide personalised advice based on your medical history, current health status, and specific pregnancy needs. When discussing magnesium supplementation, come prepared with information about your diet, any symptoms you're experiencing, and current medications or supplements you're taking.

Bring all supplement labels to your appointments so your healthcare provider can review the total daily magnesium intake from all sources, including prenatal vitamins. This helps ensure you don't exceed the recommended supplemental limit of 400 mg per day.

Your healthcare provider may assess whether you have risk factors for magnesium deficiency, such as poorly controlled diabetes, gastrointestinal disorders affecting absorption (like Crohn's disease or coeliac disease), or long-term use of certain medications. They can review your dietary intake and determine whether you're likely meeting your magnesium needs through food alone.

Routine blood testing for magnesium levels is not standard practice, as serum magnesium doesn't always reliably reflect total body stores. Testing is typically reserved for specific clinical situations where deficiency is strongly suspected.

Be specific about your reasons for considering magnesium supplementation. Whether you're experiencing leg cramps, struggling with sleep, or simply want to ensure optimal nutrition, sharing these details helps your healthcare provider give targeted advice. They can explain whether magnesium is likely to address your specific concerns or whether alternative approaches might be more appropriate.

Your midwife or GP can also guide you on the most suitable form and dosage of magnesium for your situation, taking into account any digestive sensitivities or other individual factors. If you experience any concerning side effects after starting magnesium supplementation, report them to your healthcare provider and consider reporting suspected adverse reactions through the MHRA Yellow Card Scheme.

Frequently Asked Questions