Magnesium in Pregnancy: Why You Need More and What It Does

If there is one mineral consistently falling short in pregnant women, it is magnesium.

This is not a niche nutrient with a narrow job description. Magnesium is involved in over 300 enzymatic reactions and is the fourth most abundant mineral in the human body. Nearly every cell that produces energy depends on it. When you are pregnant, your requirements increase, your body redistributes what you already have, and getting enough becomes meaningfully harder.

This article walks through what the research shows, why pregnancy changes the picture, and how to make sure you are actually covering your needs.

What Does Magnesium Actually Do?

Magnesium is a cofactor, a molecule that assists enzymes in carrying out their function, for more than 300 enzymatic reactions in the body. That number reflects just how foundational this mineral is to human physiology (de Baaij et al., 2015).

Its core roles include:

• Energy production (ATP synthesis): Magnesium is required to activate ATP (adenosine triphosphate), the molecule that powers virtually every cellular function. Without adequate magnesium, your cells cannot generate or use energy efficiently.
• Protein synthesis: Essential for building and repairing tissue, including the rapidly growing foetal tissue throughout pregnancy.
• Nerve transmission and muscle function: Magnesium regulates the electrical activity that controls nerve signals and helps muscles both contract and relax. This is why it appears so often in conversations about cramps and tension.
• Blood glucose regulation: Magnesium is involved in insulin signalling and glucose metabolism.
• Blood pressure regulation: It supports healthy vascular tone by influencing the behaviour of smooth muscle in blood vessel walls.
• Bone structure: Approximately 60% of the body's magnesium is stored in bone, where it contributes to structural integrity alongside calcium and phosphorus.

Essentially: every cell in your body that makes energy uses magnesium. And during pregnancy, your body is making an extraordinary amount of new cells.

Why Your Magnesium Requirements Increase During Pregnancy

Even before pregnancy, magnesium intake in many Western populations falls short of recommended levels. Research and national dietary survey data suggest that a significant proportion of Australians do not consistently reach their daily target (Schwalfenberg and Genuis, 2017). In pregnancy, that gap tends to widen for several reasons.

Plasma volume expansion. Your blood volume increases by up to 50% during pregnancy. This dilutes the concentration of serum magnesium, even if your absolute intake has not changed.

Foetal and placental demand. Your baby's developing bones, nervous system, and rapidly dividing cells all require magnesium. That demand is drawn primarily from your stores and intake.

Increased renal excretion. Kidney filtration increases significantly during pregnancy, and magnesium is excreted at a higher rate than in the non-pregnant state.

The Australian Nutrient Reference Values (NRVs), published by the National Health and Medical Research Council, reflect this increased need. The recommended daily intake for magnesium during pregnancy sits between 300 and 360 mg per day, depending on your age (NHMRC, 2006). This is approximately 35 mg higher than non-pregnant requirements, accounting for additional lean tissue being built during gestation.

Getting that additional magnesium from diet alone is theoretically achievable, but in practice, many women do not manage it consistently, particularly when first-trimester food aversions, nausea, or restricted eating patterns are in play.

Signs Your Magnesium May Be Low in Pregnancy

Magnesium depletion in pregnancy does not always present dramatically. It often shows up as a cluster of complaints that are easy to attribute to pregnancy itself.

Common signs associated with low magnesium during pregnancy include:

• Leg cramps, particularly at night
• Poor sleep quality or difficulty staying asleep
• Restless legs syndrome (RLS): an uncomfortable urge to move the legs, especially at rest or in the evening
• Muscle tension and tightness, particularly in the calves and back
• Anxiety, irritability, or difficulty winding down
• Constipation
• Frequent headaches
• Changes in blood pressure

If several of these sound familiar, it is worth raising your magnesium status with your healthcare provider or naturopath.

Magnesium and Leg Cramps: What the Research Actually Shows

Leg cramps are one of the most reported discomforts of pregnancy, affecting an estimated 30 to 50 percent of pregnant women. They are disruptive, often painful, and most frequently strike at night when you most need rest.

The mechanistic link between magnesium and muscle cramps is well-established: magnesium is essential for muscle relaxation. When a muscle contracts, calcium drives the action. Magnesium is what allows the muscle to release. A deficiency shifts this balance toward sustained contraction.

What does the formal research say? 

The Cochrane review by Garrison et al. (2020) on magnesium for skeletal muscle cramps concluded that the overall evidence base remains uncertain, particularly for pregnancy-related rest cramps. Some trials included in the review showed benefit over placebo; others did not demonstrate a statistically significant difference. The reviewers called for better-quality trials before firm conclusions could be drawn.

A separate Cochrane review on interventions specifically for pregnancy-related leg cramps found that magnesium supplements may reduce how frequently women experience cramps compared with placebo, though this was rated as low-certainty evidence based on the included trials.

Despite the mixed trial picture, magnesium supplementation (particularly glycinate and citrate forms) is widely used in clinical naturopathic and midwifery practice for leg cramp support. The mechanism is sound, the safety profile at therapeutic doses in pregnancy is well established, and clinical experience from practitioners is broadly positive. For most women, it is a reasonable, low-risk intervention to explore with their healthcare provider.

Sleep and Anxiety: Magnesium and Your Nervous System

Sleep in pregnancy is rarely straightforward. Between physical discomfort, frequent waking, and a mind processing the enormity of what is coming, quality rest is often elusive. Anxiety in pregnancy is also common, and far more prevalent than is often acknowledged.

Magnesium may help support both, through its role in nervous system regulation.

Magnesium binds to GABA receptors in the brain. GABA, or gamma-aminobutyric acid, is the brain's primary inhibitory neurotransmitter. When GABA is active, neural activity slows, promoting calm and facilitating sleep. Magnesium enhances GABA receptor activity, supporting this inhibitory effect through a physiological rather than pharmacological pathway.

Magnesium also blocks NMDA receptors, which are involved in excitatory nervous system activity. By moderating this pathway, adequate magnesium may help buffer the stress response and reduce neural hyperexcitability.

A systematic review by Boyle et al. (2017) found evidence suggesting a beneficial effect of magnesium supplementation on subjective anxiety and stress, although the authors noted that the quality of the existing evidence base was limited and that well-designed randomised controlled trials are needed. Research has also found associations between low magnesium levels, disrupted sleep architecture, and heightened stress responsiveness (Abbasi et al., 2012).

Magnesium is not a treatment for clinical anxiety or a sleep disorder. But for many pregnant women, supporting the nervous system with adequate magnesium is a reasonable, low-risk part of a broader approach to sleep and emotional wellbeing. Discuss what is appropriate for you with your midwife or healthcare provider.

Magnesium, Blood Pressure, and Preeclampsia: An Honest Look at the Evidence

This section requires careful language. The aim is to give an honest picture rather than an oversimplified one.

First, the established medical fact: magnesium sulfate administered intravenously is the standard treatment used in clinical settings for eclampsia, the seizure complication of severe preeclampsia. This is not a supplement claim but a well-established medical intervention that reflects how central magnesium is to neuromuscular function and cardiovascular stability.

What about dietary or supplemental magnesium and preeclampsia risk? This is a separate and more nuanced question.

Observational research suggests an association between higher dietary magnesium intake and lower risk of pregnancy-related hypertensive conditions. A systematic review and meta-analysis of observational studies found that lower magnesium intake during pregnancy was associated with gestational hypertension and preeclampsia (Schoenaker et al., 2014). A case-control study of Chinese pregnant women published in Scientific Reports found that women in the highest quartile of dietary magnesium intake had approximately 37% lower odds of preeclampsia compared with those in the lowest quartile (Scientific Reports, 2023).

However, observational associations do not establish that supplementation prevents preeclampsia. That claim has not been supported in robust interventional trials, and it would not be accurate to make it here. What can be said is that ensuring adequate magnesium intake through diet and supplementation, as part of an overall well-nourished pregnancy, is consistent with good maternal health practice.

If you have risk factors for hypertension or preeclampsia, this is a conversation to have directly with your obstetrician or midwife.

Not All Magnesium Supplements Are Equal

The form of magnesium in a supplement matters enormously. Bioavailability, how much of the mineral the body can actually absorb and use, varies widely between forms, and the cheapest option is rarely the most effective.

• Magnesium glycinate: Bound to the amino acid glycine. High bioavailability, gentle on the digestive system, and carries no laxative effect. Glycine itself has calming properties that may further support sleep. Generally considered the best form for pregnancy supplementation, particularly for sleep, muscle relaxation, and cramp support.
• Magnesium amino acid chelate (also labelled as magnesium bisglycinate, magnesium diglycinate, or magnesium glycinate) refers to magnesium bound to amino acids, which improves absorption and reduces gastrointestinal side effects compared to some other forms. This is the form used in Complete Support, chosen for its bioavailability and tolerability throughout pregnancy and postpartum.
• Magnesium citrate: Good absorption and widely available. Has a mild laxative effect, which can be genuinely useful if constipation is a concern in pregnancy. A practical and accessible option.
• Magnesium oxide: Poor bioavailability, estimated at around 4%. Primarily used as an antacid or laxative rather than for raising magnesium status. Not ideal if tissue repletion is your goal.
• Magnesium malate: Bound to malic acid. Good bioavailability and particularly well-suited to muscle and energy support.
• Magnesium threonate: Specifically researched for cognitive function and its ability to cross the blood-brain barrier. Evidence in pregnancy is limited; worth discussing with your practitioner if cognitive or mood support is a priority.
• Magnesium chloride: The form most commonly used in topical products such as sprays and flakes. Magnesium chloride is the form most commonly used in topical magnesium sprays because it is highly soluble in water, stable in solution, and has favourable skin-contact properties. This is why it is the form used in Mother Natal's Magnesium Spray.
• Magnesium stearate is not a therapeutic form of magnesium. It is a flow agent and excipient, used in tiny quantities during supplement manufacturing to prevent ingredients from sticking to machinery. You will see it listed on many supplement labels, but it does not contribute meaningfully to your magnesium intake.

When reading a supplement label, always check which form of magnesium is used, not just the listed dose. A high-dose magnesium oxide product may deliver far less usable magnesium than a lower-dose glycinate formula.

Topical Magnesium: What the Evidence Actually Supports

Topical magnesium, applied directly to the skin as a spray or oil, offers a complementary approach to oral supplementation. Research has demonstrated that the skin can absorb magnesium transdermally, with studies showing measurable increases in red blood cell magnesium following consistent topical use (Chandrasekaran et al., 2016). Applied directly to areas of muscle tension or cramping, it may also provide targeted localised relief. Many people find topical magnesium particularly useful in the evenings, applied to legs and feet before bed to support relaxation and reduce cramping overnight. Mother Natal's Magnesium Spray uses magnesium chloride for its excellent solubility and skin compatibility.

Magnesium-Rich Foods to Prioritise

Food-first is always the right foundation. Here are some of the richest dietary sources of magnesium, with approximate amounts per serve:

Food	Serving Size	Approximate Magnesium
Pumpkin seeds	30g	~150mg
Dark chocolate (70%+)	30g	~50mg
Almonds	30g	~80mg
Cashews	30g	~75mg
Black beans (cooked)	100g	~70mg
Spinach (cooked)	100g	~85mg
Avocado	half (75g)	~30mg
Quinoa (cooked)	100g	~65mg
Banana	1 medium	~32mg
Oats (dry)	40g	~50mg

One important note: cooking and food processing can significantly reduce magnesium content. Boiling vegetables leaches magnesium into the cooking water. Refined grains lose the majority of their magnesium during milling, which is why whole grain choices matter.

Getting to the 300 to 360 mg daily target through food alone during pregnancy is achievable in theory but genuinely challenging in practice, particularly if food aversions, nausea, or appetite changes are part of your first trimester experience. Many women benefit from combining a magnesium-rich diet with a quality supplement.

Magnesium After Birth: Don't Forget the Fourth Trimester

If you are breastfeeding, your magnesium requirements remain elevated. Magnesium is transferred to your baby through breastmilk, and the combined demands of sleep deprivation, physical recovery, and ongoing lactation can deplete your stores further.

Magnesium depletion in the postpartum period is associated with fatigue, muscle tension, and mood changes. These are often attributed entirely to new-parent exhaustion, but low magnesium can contribute meaningfully to how depleted you feel.

It is worth continuing a quality magnesium supplement through your postpartum recovery, particularly while breastfeeding, and reviewing your needs at your postnatal check.

Putting It Together

Magnesium is one of the most foundational minerals in the body, and pregnancy is precisely the time when the gap between what you need and what you are getting tends to widen. The good news is that this is genuinely addressable: a well-targeted diet, a quality supplement in the right form, and targeted topical support for acute cramps can make a meaningful difference.

As always, supplementation decisions during pregnancy should be made in conversation with your midwife, obstetrician, or naturopath. This article is designed to give you informed, evidence-grounded context for that conversation, not to replace it.

This article is intended for educational purposes only and does not constitute medical advice. Magnesium supplementation during pregnancy should be discussed with your qualified healthcare provider before commencing. Individual needs vary and this content does not account for your personal health history or circumstances.

Frequently Asked Questions

How much magnesium do I need during pregnancy?

The Australian NRV recommends between 300 and 360 mg of magnesium per day during pregnancy, depending on your age. This is approximately 35 mg higher than the recommendation outside of pregnancy, reflecting the additional demands of foetal development, plasma volume expansion, and increased renal excretion (NHMRC, 2006).

Is it safe to take magnesium supplements during pregnancy?

Magnesium supplementation at therapeutic doses is generally considered safe during pregnancy and is commonly used by naturopaths, midwives, and GPs as part of pregnancy care. The form and dose both matter, so it is worth discussing the right approach with your healthcare provider before starting.

What is the best form of magnesium to take during pregnancy?

Magnesium glycinate (also labelled as magnesium amino acid chelate, bisglycinate, or diglycinate) is generally considered the best option for pregnancy because of its high bioavailability and minimal digestive side effects. Magnesium citrate is a practical choice if constipation is a concern. Magnesium oxide is generally not recommended as a primary supplement, as its bioavailability is very low (around 4%) and it functions primarily as a laxative rather than a tissue-building form.

Can magnesium help with pregnancy leg cramps?

Research on this is mixed. Some randomised controlled trials report benefit from oral magnesium for pregnancy-related leg cramps, while others have not shown a statistically significant difference versus placebo. The Cochrane review (Garrison et al., 2020) rates the evidence as low certainty. Despite this, magnesium supplementation is widely used in clinical practice for leg cramp support, given its sound mechanistic rationale and good safety profile. Discuss with your healthcare provider whether it is appropriate for you.

Does magnesium support sleep in pregnancy?

Magnesium supports the nervous system through its interaction with GABA receptors, which promote calm and reduce excitatory neural activity. Research suggests associations between low magnesium levels, disrupted sleep quality, and heightened stress response. While the evidence base is still developing, magnesium glycinate is commonly used in clinical practice to help support sleep quality in pregnancy. It is not a treatment for a sleep disorder, but it can be a useful part of a broader sleep support approach.

Can I use a magnesium spray instead of taking an oral supplement?

Topical magnesium sprays and oral supplements are best thought of as complementary rather than interchangeable. Research has demonstrated measurable transdermal absorption of magnesium, and applying a spray directly to cramping or tense muscles can offer targeted localised relief. The most evidence-consistent approach is oral supplementation for overall magnesium status, with topical application as a practical complement for acute muscle discomfort.

Does magnesium help with anxiety during pregnancy?

Magnesium plays a role in nervous system regulation through its influence on GABA and NMDA receptor activity. A systematic review found evidence suggesting magnesium supplementation may help support reductions in subjective anxiety and stress, though the quality of existing evidence was noted as limited (Boyle et al., 2017). Magnesium is not a treatment for clinical anxiety. If you are experiencing significant anxiety during pregnancy, please speak with your midwife, GP, or a perinatal mental health professional.

Should I keep taking magnesium after giving birth?

Yes, particularly if you are breastfeeding. Magnesium requirements remain elevated during lactation, and the combination of physical recovery, sleep deprivation, and ongoing magnesium transfer to your baby through breastmilk can deplete your stores significantly. Continuing a quality magnesium supplement through the postpartum period and reviewing your needs at your postnatal check is reasonable practice for most women.

References

Abbasi B, Kimiagar M, Sadeghniiat K, Shirazi MM, Hedayati M, Rashidkhani B. The effect of magnesium supplementation on primary insomnia in elderly: a double-blind placebo-controlled clinical trial. Journal of Research in Medical Sciences. 2012;17(12):1161-9.

Boyle NB, Lawton C, Dye L. The effects of magnesium supplementation on subjective anxiety and stress: a systematic review. Nutrients. 2017;9(5):429.

Chandrasekaran NC, Sanchez WY, Mohammed YH, Grice JE, Roberts MS, Barnard RT. Permeation of topically applied magnesium ions through human skin is facilitated by hair follicles. Magnesium Research. 2016;29(2):35-42.

de Baaij JHF, Hoenderop JGJ, Bindels RJM. Magnesium in man: implications for health and disease. Physiological Reviews. 2015;95(1):1-46.

Garrison SR, Allan GM, Sekhon RK, Musini VM, Khan KM. Magnesium for skeletal muscle cramps. Cochrane Database of Systematic Reviews. 2020;9(9):CD009402.

Gröber U, Werner T, Vormann J, Kisters K. Myth or reality: transdermal magnesium? Nutrients. 2017;9(8):813.

National Health and Medical Research Council. Nutrient Reference Values for Australia and New Zealand. Canberra: NHMRC; 2006. Available at: www.nrv.gov.au

Schoenaker DAJM, Soedamah-Muthu SS, Callaway LK, Mishra GD. The association between dietary factors and gestational hypertension and pre-eclampsia: a systematic review and meta-analysis of observational studies. BMC Medicine. 2014;12:157.

Schwalfenberg GK, Genuis SJ. The importance of magnesium in clinical healthcare. Scientifica. 2017;2017:4179326.

Scientific Reports. The association between dietary mineral intake and the risk of preeclampsia in Chinese pregnant women: a matched case-control study. Scientific Reports. 2023. doi:10.1038/s41598-023-43481-4

Spätling L, Spätling G. Magnesium supplementation in pregnancy: a double-blind study. British Journal of Obstetrics and Gynaecology. 1988;95(2):120-5.

Zhang X, Li Y, Del Gobbo LC, Rosanoff A, Wang J, Zhang W, Song Y. Effects of magnesium supplementation on blood pressure: a meta-analysis of randomized double-blind placebo-controlled trials. Hypertension. 2016;68(2):324-33.