Safety of Magnesium Citrate at 33 Weeks Pregnancy
Yes, oral magnesium citrate can be taken at 33 weeks of pregnancy, but you should consult your healthcare provider first, as the FDA drug label specifically advises pregnant women to ask a health professional before use. 1
Key Distinction: Oral vs. Intravenous Magnesium
The evidence provided focuses primarily on intravenous magnesium sulfate for specific obstetric indications, which is fundamentally different from oral magnesium citrate used as a dietary supplement or laxative. 1
- Oral magnesium citrate is generally considered safe during pregnancy when used appropriately and is commonly used for constipation relief or magnesium supplementation. 1
- Intravenous magnesium sulfate is a therapeutic medication used for preeclampsia, eclampsia prevention, and fetal neuroprotection before 32 weeks gestation. 2, 3, 4
Magnesium Needs During Pregnancy
Magnesium requirements increase during pregnancy, and most pregnant women do not meet this increased need through diet alone. 5
- Magnesium deficiency is prevalent in women of childbearing age in both developing and developed countries. 5
- Pregnant women should be counseled to increase intake of magnesium-rich foods (nuts, seeds, beans, leafy greens) and/or supplement with magnesium at a safe level. 5
- Serum magnesium levels naturally decline after 33 weeks of gestation, with pregnancy marked by a state of hypomagnesemia (mean 1.79 ± 0.44 mg/dl until 33 weeks, then continuously declining). 6
Safety Considerations at 33 Weeks
At 33 weeks gestation, you are in the third trimester where magnesium supplementation may be particularly relevant given the natural decline in serum magnesium levels. 6
- The FDA warning about magnesium sulfate (Category D classification) specifically addresses prolonged intravenous use for more than 5-7 days to stop preterm labor, which is an unindicated and nonstandard use. 3, 4
- This warning does not apply to oral magnesium citrate used as a supplement or occasional laxative. 3, 4
- Short-term intravenous magnesium sulfate (usually less than 48 hours) remains supported by ACOG and SMFM for appropriate obstetric indications. 3, 4
When to Avoid or Use Caution
Do not use oral magnesium citrate without medical supervision if you have:
- Renal impairment, as magnesium is renally excreted and toxicity risk increases with reduced kidney function. 7, 8
- Preeclampsia or are receiving intravenous magnesium sulfate therapy, as additional oral magnesium could contribute to toxicity. 7, 9
- Oliguria (urine output <30 mL/hour), which increases magnesium toxicity risk. 7, 8
Practical Recommendations
For routine use of oral magnesium citrate at 33 weeks:
- Consult your obstetrician or healthcare provider before starting, as recommended by the FDA drug label. 1
- Use the lowest effective dose for your indication (constipation relief or supplementation). 1
- Ensure adequate hydration, particularly if using magnesium citrate as a laxative. 1
- Monitor for signs of excessive magnesium intake, though toxicity from oral supplementation is rare in women with normal kidney function. 5
Bottom Line
Oral magnesium citrate is generally safe at 33 weeks of pregnancy when used appropriately and with healthcare provider guidance, unlike the FDA warnings about prolonged intravenous magnesium sulfate for unapproved indications. 1, 3, 4 The natural decline in serum magnesium after 33 weeks may actually make supplementation beneficial, but individual assessment by your provider is essential. 5, 6