If you've searched magnesium for fertility and pregnancy with a supplement bottle in hand, you're not alone. Here's what the research actually shows.
The Short Answer
Magnesium is genuinely essential for reproductive and pregnancy health, and most of us need slightly more once we're pregnant or breastfeeding. But the evidence that a supplement changes fertility or pregnancy outcomes is far more mixed than wellness content suggests, and which form you buy matters more than people realise.
Is Magnesium Good for Fertility and Pregnancy? What the Evidence Shows
For fertility, there's more research than you'd think, just not the kind that proves a supplement helps you conceive. A 2025 US survey of over 3,000 women found low magnesium intake strengthened the link between high uric acid and infertility, a link that weakened at higher intakes. A separate 2025 study of nearly 300 infertile men found higher blood magnesium linked to better sperm count and movement. Both are patterns, not proof, low magnesium could just signal a less healthy diet overall. The closest thing to an actual trial: in a 2024 study, 13 infertile women given magnesium for four weeks saw a fertility hormone rise, but with no placebo group, that's an early signal, not solid evidence.
Pregnancy evidence is genuinely mixed. A 2014 Cochrane review of ten trials and over 9,000 women and babies found no real drop in preeclampsia risk in the trials that measured it. A newer 2022 analysis of seven trials and around 2,650 women found a 24% lower risk, mainly in higher-risk pregnancies. Two solid reviews, two different answers.
For leg cramps, a 2020 Cochrane review found the evidence a genuine shrug, some trials showed fewer cramps, others none, with overall quality rated low. That's not "it doesn't work", it's "nobody's proven it either way." If it helps you, keep taking it.
Which Form of Magnesium Should You Take?
- Oxide: cheap, but poorly absorbed. Used medically as a laxative.
- Citrate: well absorbed, also has a laxative effect at higher doses.
- Lactate, aspartate, chloride: also well absorbed
- Glycinate: widely considered the gentlest on the stomach.
There's no pregnancy-specific evidence that one well-absorbed form beats another for TTC, pregnancy or breastfeeding. Citrate or glycinate are sensible everyday picks, and citrate's laxative effect can do double duty if constipation is an issue.
Does Your Stage Change the Guidance?
Needs rise slightly in pregnancy, around 350-360mg a day per NIH versus 310-320mg otherwise, then drop back down once you're breastfeeding. In the UK, the NHS doesn't include magnesium among its routine pregnancy supplements (only folic acid and vitamin D), on the basis a varied diet covers it.
This is about oral supplements, not the magnesium sulphate given by IV in hospital for preeclampsia, eclampsia or preterm labour, that's a separate, medically managed treatment (ACOG, FDA).
Stick to the recommended amount: going over it has been linked to delayed milk coming in after birth (7).
The Bottom Line
Magnesium is genuinely important for fertility and pregnancy, and a good diet covers most of what you need. The evidence on top of that is promising but unsettled for preeclampsia, weak for leg cramps, and not there yet for fertility. That doesn't mean don't bother: there's no evidence that taking the recommended amount does any harm, and magnesium is doing plenty else for your body regardless, so it's a reasonable one to keep taking if you want to. That's the kind of nuance a Google search won't give you, and it's what we built PregSafe to sort through for you. Join our waitlist to be the first to try it.
PregSafe is not a replacement for medical advice. Always consult your healthcare provider for personalised guidance.
Sources
- Xin X, Zhang Q, Xu J, Huang J. Effect of dietary magnesium on the association between serum uric acid and female infertility. International Journal of Women's Health. 2025.
- Yahyavi SK, et al. Serum magnesium is linked with sperm concentration, motile sperm count and serum anti-Müllerian hormone in infertile men. Reproductive BioMedicine Online. 2025.
- Sundas R, et al. Effects of magnesium supplementation on anti-Mullerian hormone level in premenopausal women. Journal of Population Therapeutics and Clinical Pharmacology. 2024;31(2):298-306.
- Makrides M, et al. Magnesium supplementation in pregnancy. Cochrane Database of Systematic Reviews. 2014.
- Yuan J, Yu Y, Zhu T, Lin X, Jing X, Zhang J. Oral magnesium supplementation for the prevention of preeclampsia: a meta-analysis of randomized controlled trials. Biological Trace Element Research. 2022;200(8):3572-3581.
- Luo L, et al. Interventions for leg cramps in pregnancy. Cochrane Database of Systematic Reviews. 2020. (7) National Library of Medicine. Magnesium Aspartate. Drugs and Lactation Database (LactMed). National Institutes of Health.
