Articles
New Arrival - Creatine for women. Shop now!
Jump to:
The short answer: Published research suggests iron bisglycinate is the best-tolerated form of iron during pregnancy. Studies show it may support iron status comparably to ferrous sulfate at roughly half the dose, with significantly fewer gastrointestinal side effects. Most pharmacy-shelf iron supplements in Australia use ferrous sulfate or ferrous fumarate — cheaper forms that commonly cause constipation and nausea.
Your midwife just told you your iron is low. She said to pick up an iron supplement from the chemist. So you go to the chemist, stand in front of 15 different iron products, read three labels that make no sense, and leave with the one your mum recommended.
Two weeks later, you're constipated, nauseous, and your stools are black. Welcome to iron supplementation in Australia.
If you're searching for the best iron supplement for pregnancy in Australia, you're almost certainly searching because the one you're currently taking is making you miserable. Or because you've heard the horror stories and you want to avoid them entirely.
Here's what I want you to know up front: it doesn't have to be this way. The constipation, the nausea, the metallic taste — these are almost always caused by the form of iron, not by iron itself.
In my years of clinical practice, the number one reason women stopped taking their iron was constipation. The number two reason was nausea. Both problems were nearly always resolved by switching to a different form. Not a different dose. Not a different time of day. The form.
I remember one patient — 26 weeks pregnant, ferritin of 11, exhausted, breathless climbing her own stairs. Her GP had prescribed a high-dose ferrous sulfate tablet. She lasted nine days before the constipation became unbearable and she stopped. When I saw her, she'd been off iron for a month and her levels had dropped further. We switched her to iron bisglycinate. Six weeks later, her ferritin had climbed to 28 and she told me she'd forgotten what it felt like to not be exhausted. That's not the iron "working better" — it's the iron being tolerable enough to actually take every day.
This guide will walk you through the forms, the research, and how to choose a gentle iron supplement for pregnancy you'll actually take consistently.
The word "iron" on the front of the bottle tells you almost nothing. What matters is the compound listed on the back — and it determines everything: how much your body absorbs, how your gut reacts, and whether you'll still be taking it in two weeks or whether it'll be collecting dust in your bathroom cabinet.
Here's what you need to know about each form.
The cheapest and most widely used form of supplemental iron worldwide. It's the default GP recommendation because the research base is extensive and it's been prescribed for decades — there's nothing wrong with the evidence behind it. Absorption is reasonable.
The problem is tolerability.
Ferrous sulfate comes with a high rate of constipation, nausea, abdominal cramping, and black stools. A 2024 study comparing iron forms in pregnant women found that ferrous sulphate 50mg had a black stool frequency of 31% — the highest of any form tested (Milman et al., Nutrients, 2024). In the same study, constipation and laxative use were also highest in the sulfate group.
Here's what I see in practice: women are prescribed ferrous sulfate, experience side effects, stop taking it, and conclude that "iron doesn't agree with them." In most cases, it's ferrous sulfate that doesn't agree with them — not iron. The compliance problem is the real clinical issue. An iron supplement you can't tolerate is an iron supplement that doesn't work.
Best for: Severe deficiency requiring rapid correction under medical supervision — if tolerated.
The catch: Many women can't tolerate it consistently, which undermines the entire point of supplementation.
A step up from sulfate in tolerability, and the second most common form you'll find on Australian pharmacy shelves. It's still a ferrous iron salt, meaning it's absorbed through the same ionic pathway as sulfate — but it tends to cause somewhat fewer side effects.
The same 2024 Milman study showed fumarate at 40mg had a 22% rate of black stools — better than sulfate's 31%, but still significant for a supplement you need to take every day for months. The overall GI side effect profile was similar to sulfate at equivalent doses.
Best for: Mild-to-moderate supplementation when bisglycinate isn't available. A reasonable second choice.
The catch: Still a ferrous salt. If you're already struggling with constipation from iron, switching from sulfate to fumarate may not be enough of a change to resolve it.
Iron bound to two molecules of the amino acid glycine. This is the form with the strongest published evidence for both absorption and tolerability during pregnancy — and it's the form I've recommended most often in clinical practice over the past decade.
The evidence is substantial:
Absorption: A Danish RCT found that ferrous bisglycinate at 25mg was comparably effective to ferrous sulfate at 50mg in supporting iron status during pregnancy (Milman et al., 2014). Half the dose, comparable outcomes. This means bisglycinate has approximately twice the bioavailability of sulfate — your body gets more from less.
Tolerability: A systematic review and meta-analysis of 17 RCTs published in Nutrition Reviews found that ferrous bisglycinate was associated with higher haemoglobin concentrations and fewer GI adverse events among pregnant women compared to other iron supplements. In the pregnancy-specific analysis (9 RCTs), the incidence rate ratio for gastrointestinal adverse events was 0.36 (95% CI: 0.17–0.76) — suggesting a 64% reduction in GI side effects compared to traditional iron salts (Name et al., 2023).
Efficacy: A 2017 double-blind RCT of 187 pregnant women with iron deficiency found that the bisglycinate group achieved a mean haemoglobin increase of 2.48 g/dL over 8 weeks, compared to 1.32 g/dL in the ferrous glycine sulfate group — with significantly fewer adverse effects (Abdel Moety et al., 2017).
Black stools: The 2024 Milman study found bisglycinate at 25mg had a black stool frequency of just 8%, compared to 22% for fumarate and 31% for sulfate.
Why does bisglycinate work so differently? Because it's absorbed through a completely different pathway. Ferrous salts (sulfate, fumarate) rely on ionic iron absorption, which is inefficient and leaves a lot of unabsorbed iron sitting in your gut — causing the constipation, nausea, and dark stools. Bisglycinate is absorbed via the dipeptide transport pathway in the small intestine, meaning more iron gets into your bloodstream and less irritates your colon.
Best for: Pregnancy supplementation, women with sensitive stomachs, anyone who's tried iron and stopped because of side effects.
The catch: More expensive per tablet than ferrous salts. But given the higher absorption, you need a lower dose — so the cost per milligram of absorbed iron is actually comparable or better.
This is the form we use in IronBiotic.
A non-ionic iron complex with genuinely fewer GI side effects than ferrous salts — that's its real strength, and it's why many Australian GPs and obstetricians have started recommending it as an alternative to sulfate.
However, there are limitations. Doses are typically high (100mg+ elemental iron), and absorption of polymaltose iron is generally lower than chelated forms like bisglycinate. Some research suggests the high dose partly compensates for lower bioavailability — meaning you're taking more iron to absorb less of it, which raises the question of whether you're getting the efficiency you're paying for.
Best for: Women who need high-dose iron supplementation under medical guidance and have struggled with ferrous salts.
The catch: 100mg is more iron than many women need for routine pregnancy supplementation. The absorption debate means you may not be getting as much usable iron as the label suggests.
Very gentle, naturally occurring iron from spring water. Well-tolerated with minimal GI effects — genuinely the kindest option for women who are extremely sensitive to supplemental iron. I recommend liquid iron regularly for women with borderline levels who need gentle maintenance rather than correction.
Best for: Iron maintenance, very mild low iron, women who can't swallow tablets, first trimester when nausea makes everything difficult.
The catch: Typically around 5mg per sachet, which is often not enough to address meaningful iron deficiency during pregnancy. If your ferritin is below 30, liquid iron alone may not shift it. You'd need 3–4 sachets daily to approach a useful dose, which becomes expensive quickly.
|
Iron Form |
Typical Dose |
Relative Absorption |
GI Side Effects |
Black Stools (2024 study) |
Best For |
|---|---|---|---|---|---|
|
Iron bisglycinate |
18–25mg |
Highest (≈2× sulfate) |
Minimal — gentle |
8% |
Pregnancy, sensitive stomachs |
|
Ferrous sulfate |
50–325mg |
Good |
High — constipation, nausea |
31% |
Severe deficiency (if tolerated) |
|
Ferrous fumarate |
12–65mg |
Moderate |
Moderate |
22% |
Mild supplementation |
|
Iron polymaltose |
100mg+ |
Lower than bisglycinate |
Low–moderate |
Not tested in this study |
High-dose medical use |
|
Liquid iron |
~5mg |
Low–moderate |
Minimal |
N/A |
Maintenance, very mild low iron |
Rather than recommending brands, here's how to think about which form is right for you:
If you've never taken iron before and want to avoid side effects: Start with iron bisglycinate. The published evidence for tolerability during pregnancy is strongest for this form, and you can take a lower dose because absorption is higher.
If you're currently taking a ferrous sulfate or fumarate and it's making you miserable: Switch to bisglycinate. This is the single most common change I make in practice, and the single change that most consistently resolves the constipation and nausea women experience.
If your GP has prescribed high-dose iron (100mg+) for significant deficiency: Iron polymaltose may be appropriate under their guidance. But ask whether a lower dose of bisglycinate might achieve the same result with fewer side effects — some practitioners aren't aware of the bisglycinate research.
If your iron is borderline and you just want to maintain levels: iron bisglcyinate again is a fantastic choice.
If you're in the first trimester and everything makes you nauseous: Bisglycinate or liquid iron.
I had a patient who'd been on high-dose ferrous sulfate for three months with almost no improvement in her ferritin. When we looked at what was happening, she was taking it inconsistently — three days on, four days off — because the constipation was so bad she'd stop, feel better, and start again. We switched to bisglycinate and she took it every second day without issues. Her ferritin moved within six weeks. Compliance is the variable most iron conversations miss.
This is where I'll talk about my own product — with the context you now have about the forms.
IronBiotic uses iron bisglycinate (18mg elemental iron) because the published evidence on this form — across absorption, tolerability, and pregnancy-specific outcomes — is the strongest of any oral iron form available.
It also includes a Bifidobacterium longum probiotic to support healthy digestive function during iron supplementation, vitamin C to support dietary iron absorption, activated B vitamins (methylfolate, methylcobalamin, P5P) to support haemoglobin formation, and copper and beta-carotene to help maintain iron levels in the body.
IronBiotic is TGA-listed (AUST L, ARTG ID 509854) and designed as a companion to EverNatal — an intentionally iron-free prenatal. The logic is simple: not every woman needs the same iron dose. Some need none. Some need 18mg. Some need more. Your prenatal shouldn't force a fixed iron dose on you — it should give you the flexibility to add what you individually need, guided by your blood results.
Always read the label and follow the directions for use.
Not every pregnant woman needs the same dose, and this is where blanket recommendations cause real problems.
The Australian RDI for iron during pregnancy is 27mg per day. Most women get some iron from food — red meat, legumes, dark leafy greens, fortified cereals. The supplemental gap varies woman to woman.
The only way to know your gap is a full iron panel — not just haemoglobin. Here's the difference, and it matters:
Ferritin — your iron stores. The most important number and the most commonly undertested. If your ferritin is dropping, you're depleting your reserves — even if your haemoglobin still looks "normal." Aim for above 30 mcg/L during pregnancy; many practitioners prefer above 50 mcg/L. Read more about ferritin vs iron — they're not the same thing.
Transferrin saturation — how much of your iron transport protein is carrying iron. Below 20% can indicate iron deficiency before haemoglobin drops.
Haemoglobin — the number most GPs test routinely. Generally, above 110 g/L in pregnancy is considered adequate. But haemoglobin is a late marker — by the time it falls, you've been depleted for a while. If your ferritin isn't improving despite supplementation, read 7 reasons your ferritin isn't improving.
Download our blood test checklist for a printable guide to take to your GP.
Take on an empty stomach if tolerated. Iron absorbs best between meals. If that causes nausea, take it with a small vitamin C-rich snack — a few strawberries, an orange, capsicum — to support absorption.
Avoid taking with calcium, coffee, tea, or dairy. These can reduce iron absorption. If your prenatal contains calcium or zinc, space your iron at least 2 hours apart. A practical approach: EverNatal with breakfast, iron in the afternoon.
Space from magnesium. If you're taking magnesium in the evening, your afternoon iron and evening magnesium are naturally separated.
Consider alternate-day dosing. Emerging research on hepcidin regulation suggests that taking iron every other day may improve fractional absorption. Iron triggers hepcidin release (a hormone that reduces iron absorption for about 24 hours). By dosing every other day, you take iron when hepcidin is low. Discuss with your practitioner — this may be appropriate for maintenance rather than correcting significant deficiency.
Be consistent. Iron levels build gradually. Most women notice energy improvements within 2–4 weeks, but ferritin takes 6–12 weeks to rise meaningfully. Don't give up after a week.
Blood work is the definitive answer, but your body gives signals too. If you tick several of these during pregnancy, get your full iron panel checked:
Fatigue that's disproportionate — even for pregnancy
Breathlessness climbing stairs or during mild exertion
Heart palpitations or racing heart at rest
Pale skin, pale inner eyelids, pale nail beds
Restless legs, especially at night
Craving ice, dirt, or chalk — this is called pica, and it's one of the most specific indicators of iron deficiency
Dizziness or lightheadedness when standing
Poor concentration or brain fog
Brittle nails or increased hair shedding
The ice-crunching one surprises people, but it's genuinely one of the most reliable informal signs I see in practice. If you're compulsively crunching ice, get your iron tested promptly — pica often appears before haemoglobin drops into the "deficient" range on standard blood work.
Published research suggests iron bisglycinate has the strongest evidence for tolerability during pregnancy. A 2023 meta-analysis of 17 RCTs found it was associated with higher haemoglobin concentrations and 64% fewer GI adverse events compared to traditional iron salts in pregnant women (Name et al., Nutrition Reviews, 2023). A Danish RCT showed 25mg of bisglycinate supported iron status comparably to 50mg of ferrous sulfate — with fewer side effects (Milman et al., 2014).
Iron-related constipation is primarily caused by unabsorbed iron reaching the lower gut, where it disrupts the microbiome and slows bowel transit. Ferrous sulfate has the highest rate of this because a significant portion passes through unabsorbed. Iron bisglycinate is absorbed via the dipeptide transport pathway in the small intestine, meaning less unabsorbed iron reaches the colon. If your iron supplement is causing constipation, the form is almost certainly the problem — not iron itself.
The Australian RDI is 27mg per day, but your individual need depends on your blood results. Some women enter pregnancy with excellent stores and don't need supplemental iron for months. Others need it from the start. Get a full iron panel — ferritin, transferrin saturation, haemoglobin — and work with your practitioner. This is why iron is best dosed individually as a separate supplement.
You can, but spacing them apart may improve absorption. Iron competes with other minerals (calcium, zinc, magnesium) for the same transport pathways. EverNatal is iron-free by design — take it with breakfast, and IronBiotic separately in the afternoon.
Most women notice energy improvements within 2–4 weeks. Ferritin takes 6–12 weeks to rebuild. If levels haven't improved after 8–12 weeks of consistent supplementation, talk to your practitioner — you may need a dose adjustment, a different form, or investigation into absorption issues. Read more: 7 reasons your ferritin isn't improving.
Yes. Iron bisglycinate has been used in multiple randomised controlled trials involving pregnant women — including Milman et al. (2014), Abdel Moety et al. (2017), and Sak et al. (2022) — with no safety concerns reported. IronBiotic is TGA-listed (AUST L, ARTG ID 509854) and manufactured to Australian regulatory standards. As with any supplement during pregnancy, advise your healthcare provider.
Ferrous sulfate is the cheapest and most widely prescribed form — good absorption, but high rates of constipation, nausea, and black stools (31% in a 2024 pregnancy study). Iron bisglycinate is absorbed via a different pathway (the dipeptide transporter), achieves comparable results at roughly half the dose, and was associated with just 8% black stools in the same study. The trade-off is cost per tablet — bisglycinate costs more, but you need less of it because more is absorbed.
Many women should. Birth involves blood loss — sometimes significant — and postpartum iron depletion is extremely common yet routinely overlooked. Get a full iron panel at 6–8 weeks postpartum. Many of the symptoms women attribute to "normal new mum exhaustion" — bone-deep fatigue, breathlessness, brain fog — may actually be correctable iron deficiency.
The best iron supplement for pregnancy is the one you'll actually take — consistently, without dreading it. If your current iron is sitting in your bathroom cabinet untouched because it makes you feel terrible, the form is almost certainly the problem.
When you're choosing an iron supplement, flip the bottle over. Look at the form. If it says ferrous sulfate or ferrous fumarate, you're taking a form that the published research associates with higher rates of constipation, nausea, and black stools. If it says iron bisglycinate (or ferrous bisglycinate), you're taking the form with the strongest evidence for tolerability and absorption during pregnancy.
IronBiotic is a TGA-listed supplement (AUST L) designed to support healthy iron levels and digestive comfort. I formulated it as a companion to EverNatal — an intentionally iron-free prenatal — because iron should be dosed individually, guided by your blood results, not one-size-fits-all.
Get your iron panel tested. Know your ferritin. And choose a form your body can use — and that you'll actually take.
— Melanie Nolan, BHSc Naturopathy Founder, Naternal Vitamins
Always read the label and follow the directions for use. Advise your doctor of any medicine taken during pregnancy, particularly in your first trimester. Vitamin and mineral supplements should not replace a balanced diet.
References:
Name HN et al. (2023). 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. Nutrition Reviews, 81(8), 904–920.
Milman N, Jønsson L, Dyre P, Pedersen PL, Larsen LG (2014). 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, 42(2), 197–206.
Milman N et al. (2024). Low-Dose Prophylactic Oral Iron Supplementation in Pregnancy: Results From Two Randomized Studies. Nutrients, 16(22), 3946.
Abdel Moety GA et al. (2017). Efficacy of ferrous bis-glycinate versus ferrous glycine sulfate in the treatment of iron deficiency anemia with pregnancy: a randomized double-blind clinical trial. J Maternal-Fetal & Neonatal Medicine, 30(12), 1440–1444.
Sak S et al. (2022). Efficacy and Safety of Ferrous Bisglycinate and Folinic Acid in the Control of Iron Deficiency in Pregnant Women. Nutrients, 14(3), 463.
10 min read
10 min read
Published research suggests iron bisglycinate is the best-tolerated form of iron during pregnancy. Studies show it may support iron status comparably to ferrous sulfate at roughly half the dose, with significantly fewer gastrointestinal side effects. Most pharmacy-shelf iron supplements in Australia use ferrous sulfate or ferrous fumarate — cheaper forms that commonly cause constipation and nausea.
