Let us address this directly. Most prenatal vitamins include iron. Mothersense Prenatal+ does not. If that surprised you when you first looked at our label, you are not alone. It is the single most common question we receive, and it deserves a thorough answer.
We did not leave iron out because we think it is unimportant. Iron is one of the most critical nutrients in pregnancy. We left it out because we believe it is too important to guess at.
Iron Is Essential. The Right Dose Is Individual.
Iron plays a central role in pregnancy. It is required for hemoglobin production, which supports the nearly 50 percent increase in maternal blood volume that occurs between conception and delivery. It is essential for oxygen transport to the placenta and developing fetus. It supports fetal brain development, particularly during the second and third trimesters when neural tissue is growing rapidly.
The challenge is that iron needs vary more dramatically from woman to woman than nearly any other prenatal nutrient. A woman who enters pregnancy with robust iron stores, consumes red meat regularly, and has no history of heavy menstrual bleeding may need little or no supplemental iron. A woman who is vegetarian, has a history of anemia, carries twins, or has closely spaced pregnancies may need a significant amount.
The difference between those two women is not subtle. One may thrive on zero supplemental iron. The other may require 60 mg or more per day. A fixed-dose prenatal cannot serve both of them well.
The Problem with a One-Size-Fits-All Approach
When a prenatal includes a standard dose of iron (typically 27 to 30 mg as ferrous sulfate or ferrous fumarate), it makes an assumption about every woman who takes it. That assumption is that she needs supplemental iron, and that she needs a specific amount.
For women who do need it, that dose may be adequate, insufficient, or occasionally too much. For women who do not need it, the consequences are not trivial.
A systematic review and meta-analysis of 43 randomized controlled trials involving 6,831 adults, published in PLOS ONE, found that ferrous sulfate supplementation was associated with 2.6 times the odds of gastrointestinal side effects compared to placebo or intravenous iron (Tolkien et al., 2015). In the pregnancy-specific subgroup analysis of seven trials involving 1,028 women, the odds ratio rose to 3.33. The most commonly reported symptoms were constipation, nausea, and diarrhea.
These are the very symptoms that already plague early pregnancy. Adding an iron supplement on top of first-trimester nausea can push women to stop taking their prenatal altogether. In pregnancy, adherence with ferrous sulfate has been reported at only 70 to 90 percent due to adverse effects. A prenatal that a woman stops taking provides zero nutritional benefit, regardless of what the label says.
Iron Can Interfere with Other Essential Nutrients
Beyond digestive tolerance, there is a well-documented interaction between iron and other minerals when taken simultaneously. Iron and zinc compete for the same intestinal absorption pathways. Research published in the Journal of Nutrition demonstrated that prenatal iron supplements adversely influenced zinc absorption during pregnancy, with women in the iron-supplemented group showing lower zinc absorption than unsupplemented controls (O'Brien et al., 2000).
Iron also competes with calcium and magnesium for absorption. Data from the National Academy of Sciences' review of prenatal nutrition found that calcium carbonate and magnesium oxide are particularly inhibitory to iron absorption when included in the same supplement (Institute of Medicine, 1990). The reverse is also true. High-dose iron in a multivitamin formula can reduce the absorption of calcium, magnesium, and zinc that the supplement is designed to deliver.
This creates a formulation paradox. Including iron in a comprehensive prenatal can compromise the absorption of the other minerals in the same capsule. Separating iron allows all of the remaining minerals to be absorbed without competition, and it allows iron to be taken at a different time of day for optimal absorption on its own.
Not Every Woman Needs Supplemental Iron
While iron deficiency is common during pregnancy, it is not universal. Several populations may not benefit from routine supplementation, and in some cases, supplemental iron may cause harm.
Women with hereditary hemochromatosis, a condition affecting roughly 1 in 200 people of Northern European descent, absorb and store excess iron. For these women, additional iron supplementation during pregnancy can accelerate iron overload and damage organs including the liver and heart.
Women who enter pregnancy with ferritin levels above 70 to 80 ng/mL typically have adequate stores to support the increased demands of the first and second trimesters without supplementation. Their needs may be fully met by dietary intake alone.
Women who are not currently menstruating (for example, those who conceived while breastfeeding a previous child and did not resume menses) may have preserved iron stores that make supplementation unnecessary.
The only reliable way to determine whether a woman needs supplemental iron, and how much, is through laboratory testing. A serum ferritin level, ideally paired with a complete blood count, provides a clear picture of iron status and can be repeated throughout pregnancy to guide adjustments.
This Is a Design Choice, Not a Shortcut
We want to be transparent about what this decision is and what it is not.
It is not a cost-saving measure. Iron is one of the least expensive ingredients in any supplement formula. Removing it saves pennies. Including it would have been far easier from a marketing perspective, because it eliminates the single most common objection a consumer raises when comparing prenatal labels.
We removed iron because doing so makes the rest of the formula work better and because we believe iron dosing should be guided by clinical data, not by a default assumption.
Without iron competing for absorption in the same serving, the magnesium, calcium, and zinc in Mothersense are free to use their intestinal transport pathways without interference. Without iron irritating the gut lining, the entire formula is gentler on digestion. And without a fixed dose of iron locked into the product, every woman has the freedom to supplement iron at exactly the level her body requires, in the form her provider recommends, at the time of day that optimizes its absorption.
What We Recommend Instead
If you are pregnant, planning to become pregnant, or currently breastfeeding, we strongly recommend the following approach to iron.
First, ask your provider to test your serum ferritin and complete blood count early in pregnancy (or during preconception care if possible). These tests reveal whether your iron stores are adequate, borderline, or depleted.
Second, if supplementation is indicated, work with your provider to determine the correct dose and form. Ferrous bisglycinate (chelated iron) has been shown to be as effective as ferrous sulfate at half the dose, with significantly fewer gastrointestinal side effects (Milman et al., 2014). Many women find it far more tolerable than conventional iron salts.
Third, take your iron supplement at a different time from your prenatal. Separating iron from calcium, magnesium, and zinc by at least two hours allows each mineral to be absorbed more efficiently.
Fourth, retest your levels at intervals recommended by your provider. Iron needs change throughout pregnancy. What is adequate in the first trimester may be insufficient in the third.
The Philosophy Behind the Decision
Every ingredient in Mothersense Prenatal+ was chosen with intention. Some nutrients, like methylfolate, choline, DHA, and magnesium, are needed by virtually every pregnant woman in roughly similar amounts. These belong in a prenatal.
Iron is different. It is needed by many women, but the amount varies by a factor of ten or more depending on individual physiology, diet, and medical history. A nutrient with that degree of variability does not belong in a one-size-fits-all formula. It belongs in a conversation between a woman and her provider, guided by laboratory data and adjusted over time.
We would rather you get the right dose for your body than a generic amount that may be too much, too little, or unnecessary. That is not a gap in our formula. It is the point of it.
This article is for informational purposes only and is not intended to diagnose, treat, cure, or prevent any disease. Always consult your healthcare provider before starting or changing any supplement regimen.
References
- Tolkien Z, Stecher L, Mander AP, Pereira DIA, Powell JJ. Ferrous sulfate supplementation causes significant gastrointestinal side-effects in adults: a systematic review and meta-analysis. PLOS ONE. 2015;10(2):e0117383. https://doi.org/10.1371/journal.pone.0117383
- O'Brien KO, Zavaleta N, Caulfield LE, Wen J, Abrams SA. Prenatal iron supplements impair zinc absorption in pregnant Peruvian women. Journal of Nutrition. 2000;130(9):2251–2255. https://doi.org/10.1093/jn/130.9.2251
- Institute of Medicine Committee on Nutritional Status During Pregnancy and Lactation. Iron nutrition during pregnancy. In: Nutrition During Pregnancy: Part I Weight Gain, Part II Nutrient Supplements. Washington, DC: National Academies Press; 1990.
- Milman N, Jonsson L, Dyre P, Grubbe Dam P, Eckhoff Helgstrand GH. Ferrous bisglycinate 25 mg iron is as effective as ferrous sulfate 50 mg iron in the prophylaxis of iron deficiency and anemia during pregnancy in a randomized trial. Journal of Perinatal Medicine. 2014;42(2):197–206. https://doi.org/10.1515/jpm-2013-0153
- Milman N, Bergholt T, Eriksen L, et al. Low-dose prophylactic oral iron supplementation (ferrous fumarate, ferrous bisglycinate, and ferrous sulphate) in pregnancy is not associated with clinically significant gastrointestinal complaints: results from two randomized studies. Journal of Pregnancy. 2024;2024:1716798. https://doi.org/10.1155/2024/1716798
- Name JJ, Vasconcelos AR, Bhutani KK. The effects of oral ferrous bisglycinate supplementation on hemoglobin and ferritin concentrations in adults and children: a systematic review and meta-analysis of randomized controlled trials. Journal of Nutrition. 2023;153(6):1738–1752. https://doi.org/10.1016/j.tjnut.2023.03.033
- Harvey LJ, Dainty JR, Hollands WJ, et al. Effect of high-dose iron supplements on fractional zinc absorption and status in pregnant women. American Journal of Clinical Nutrition. 2007;85(1):131–136. https://doi.org/10.1093/ajcn/85.1.131
- Sandstrom B, Davidsson L, Cederblad A, Lonnerdal B. Oral iron, dietary ligands and zinc absorption. Journal of Nutrition. 1985;115(3):411–414. https://doi.org/10.1093/jn/115.3.411
- Georgieff MK. Iron deficiency in pregnancy. American Journal of Obstetrics and Gynecology. 2020;223(4):516–524. https://doi.org/10.1016/j.ajog.2020.03.006
- Peña-Rosas JP, De-Regil LM, Garcia-Casal MN, Dowswell T. Daily oral iron supplementation during pregnancy. Cochrane Database of Systematic Reviews. 2015;(7):CD004736. https://doi.org/10.1002/14651858.CD004736.pub5