Can a pregnant woman take magnesium supplements?

Can Pregnant Women Take Magnesium Supplements?

Yes, pregnant women can safely take magnesium supplements, and supplementation may be beneficial for reducing certain pregnancy complications, though the evidence for routine supplementation remains mixed. 1, 2

Safety Profile

• Oral magnesium supplementation is generally safe during pregnancy when used at appropriate doses, with multiple clinical trials demonstrating no significant maternal harm 2
• FDA labeling for over-the-counter magnesium products (citrate and glycinate) advises consulting a healthcare professional before use during pregnancy, but does not contraindicate use 3, 4
• The recommended dietary allowance for magnesium during pregnancy is 450 mg daily, yet most pregnant women consume only 35-58% of this amount through diet alone 5

Clinical Benefits

Magnesium supplementation during pregnancy may reduce several complications:

• Reduced risk of preeclampsia in high-risk women when combined with calcium supplementation (1.5-2 g elemental calcium daily) in those with low calcium intake (<800 mg/day) 6
• Lower rates of pregnancy complications including intrauterine growth restriction, preterm labor, and pregnancy-induced hypertension when adequate supplementation is provided 7
• Improved neonatal outcomes including fewer infants with Apgar scores less than 7 at five minutes, less meconium-stained liquor, and reduced mild hypoxic-ischemic encephalopathy 2
• Decreased maternal hospitalizations during pregnancy (35% reduction) 2

Dosing Recommendations

Typical supplementation regimens used in clinical trials include:

• Magnesium citrate: 340-365 mg daily starting from 9-18 weeks' gestation 2
• Magnesium aspartate: 15 mmol daily from early pregnancy 2
• Combined supplementation: 200 mg effervescent magnesium plus 100 mg from prenatal multivitamin showed superior outcomes 7

Important Caveats

The evidence has limitations that warrant caution:

• A 2014 Cochrane review of 10 trials (9,090 women) found no significant difference in perinatal mortality, small-for-gestational age, or preeclampsia when analyzing all studies together 2
• When restricted to only high-quality trials, none of the primary outcomes showed significant benefit 2
• One large trial showed a possible increased risk of neonatal death, though this was likely due to congenital anomalies unrelated to magnesium supplementation 2

Magnesium supplementation does NOT effectively treat leg cramps in pregnancy, despite common belief—a randomized trial of 360 mg daily showed no benefit for this indication 8

Therapeutic Use in Pregnancy Complications

Magnesium sulfate (intravenous) has established therapeutic roles:

• Prevention of eclamptic seizures in women with HELLP syndrome and severe hypertension 6
• Neuroprotection for preterm delivery before 32 weeks' gestation 6
• Standard protocols involve loading and maintenance doses per local guidelines 6

Critical safety consideration: Iatrogenic magnesium toxicity can occur in pregnant women receiving IV magnesium sulfate for preeclampsia/eclampsia, particularly if oliguria develops—continuing administration during oliguria significantly increases toxicity risk 9

Practical Approach

For routine supplementation:

• Pregnant women should be counseled to increase dietary magnesium through nuts, seeds, beans, and leafy greens 1
• Supplementation at safe levels (300-400 mg daily) is reasonable given widespread dietary inadequacy 1, 5
• Women at high risk for preeclampsia should receive aspirin 100-150 mg daily from week 12 plus calcium supplementation if dietary calcium is low 6

Monitor for adequacy: Most prenatal vitamins contain only 100 mg magnesium or less, which is insufficient to meet increased pregnancy needs 5