Magnesium and pregnancy: needs, deficiencies, and magnesium-rich foods for pregnant women

By: Solène Limongi (Nutritionniste et diététicienne) — 22/02/2026

The role of magnesium during pregnancy

Magnesium is an essential mineral involved in more than 300 enzymatic reactions in the body. It is essential for the proper functioning of muscles, nerves, and the immune system. During pregnancy, its roles are particularly important:

• Muscle and nerve function: magnesium regulates muscle contraction and relaxation. A deficiency can promote cramps (very common in the 3^rd trimester) and uterine hyperexcitability.
• Blood pressure regulation: magnesium contributes to vasodilation and maintaining normal blood pressure. Intravenous magnesium sulfate is the reference treatment for eclampsia, with a 58% reduction in seizure risk according to the Magpie trial (10,141 women, The Lancet 2002).
• Glucose metabolism: magnesium plays a role in insulin sensitivity. A 2022 meta-analysis (Qu et al., 4 trials, 198 participants) showed significant improvement in fasting blood glucose and insulin resistance in supplemented women with gestational diabetes.
• Fetal neuroprotection: magnesium sulfate administered before preterm delivery (before 30 WA) reduces the risk of cerebral palsy in the newborn (Cochrane 2024, high-certainty evidence).
• Protein and DNA synthesis: magnesium is necessary for the synthesis of proteins, nucleic acids, and hormones, processes that are particularly active during fetal development.

Serum magnesium levels naturally decrease throughout pregnancy: on average from 0.93 mmol/L before conception to 0.63 mmol/L in the 3^rd trimester (Morton 2018), due to hemodilution, increased fetal needs, and increased renal excretion.

Magnesium needs and recommended doses during pregnancy

Recommendations vary depending on health authorities. Here are the main references:

Important point: ANSES and EFSA do not increase the dose during pregnancy (300 mg/day for all adult women), while US authorities (NIH/IOM) recommend an increase of +40 mg/day, i.e., 350 to 360 mg/day depending on age. The safety limit applies only to magnesium from dietary supplements, not from food.

Magnesium deficiency: frequency and symptoms in pregnant women

Magnesium deficiency is common in the general population and even more so in pregnant women. According to the French SU.VI.MAX study (13,500 adults, coordinated by INSERM), 77% of French women have magnesium intakes below recommended dietary allowances, and 23% consume less than two-thirds of the RDA.

Among pregnant women specifically, data vary depending on the populations studied: a German study reports 14.5% frank deficiency and 33% sub-optimal levels, while Russian cohorts (MAGIC and MAGYN studies, 983 women) find a prevalence of 34 to 79% depending on the threshold used (Morton 2018).

Symptoms of magnesium deficiency during pregnancy include:

• Muscle cramps, particularly in the calves (especially at night in the 3^rd trimester)
• Fatigue and irritability
• Sleep disturbances
• Contractions felt as abdominal tightening
• Tingling or numbness of the extremities
• Nausea and loss of appetite

Serum magnesium is not a good reflection of body stores (only 1% of total magnesium is in the blood). Diagnosis is therefore based primarily on clinical symptoms and assessment of dietary intake.

Risks of magnesium deficiency during pregnancy

Magnesium deficiency during pregnancy is associated with several complications, documented in the medical literature:

Important nuance: the Cochrane 2014 review (Makrides et al., 10 trials, 9,090 women) concludes that the evidence is still insufficient to recommend routine magnesium supplementation during pregnancy. The WHO also does not recommend routine supplementation. This means that the priority should be a balanced diet, and that supplementation should be discussed on a case-by-case basis with your doctor or midwife.

Magnesium-rich foods for pregnant women

The best strategy to meet your magnesium needs is a varied diet rich in naturally magnesium-rich foods. Here are the main dietary sources (CIQUAL/ANSES data):

Very rich sources (> 200 mg per 100 g)

Rich sources (50-200 mg per 100 g)

Practical tip: a handful of almonds (30 g) as a snack + a serving of spinach at dinner + whole wheat bread at breakfast already provides you with about 200 mg of magnesium, or two-thirds of the recommended intake. See our article on the ideal breakfast for pregnant women for magnesium-rich meal ideas.

Magnesium-rich mineral waters

Mineral water is an often overlooked but easy-to-integrate daily source of magnesium. Some French mineral waters are particularly rich:

Drinking 1.5 liters of Hépar per day alone covers nearly 60% of your daily magnesium needs, with no caloric intake. Hépar water also has a mild laxative effect that can help relieve constipation, which is common during pregnancy.

Magnesium supplements: when and which ones to choose?

Supplementation is not routinely recommended during pregnancy (by neither the WHO nor ANSES). It may however be considered in case of confirmed deficiency, debilitating cramps, or premature contractions, on medical advice. Not all forms of magnesium are equal:

Vitamin B6 (pyridoxine) is often combined with magnesium in French supplements (Magnesium B6 type). It promotes magnesium entry into cells. This combination is frequently prescribed by doctors and midwives in France.

Recommended dosage: do not exceed 250 mg/day in supplements (ANSES/EFSA limit). Start with a dose of 150-200 mg/day and adjust based on tolerance. The first sign of overdose is diarrhea.

Safety and drug interactions

Dietary magnesium poses no risk of overdose. For supplements, respect the limit of 250 mg/day (EFSA) or 350 mg/day (NIH). Some interactions should be noted:

• Iron: magnesium and iron compete for intestinal absorption. If you are taking an iron supplement (common during pregnancy), take magnesium at a different time of day, with at least 2 hours between them.
• Antibiotics (tetracyclines, quinolones): magnesium forms chelates that reduce their absorption. Take magnesium at least 2 hours before or 4-6 hours after the antibiotic.
• PPIs (omeprazole and others): prolonged use (more than one year) can cause hypomagnesemia. Inform your doctor if you are taking a PPI long-term.
• Kidney failure: contraindication to magnesium supplementation due to the risk of hypermagnesemia.

In all cases, consult your doctor or midwife before starting a magnesium supplement during pregnancy. ANSES recommends the utmost caution with dietary supplements in pregnant women.