Iron in Pregnancy: How Much You Need, Common Side Effects & How to Prevent Constipation

Written by Róisín Cahill, MPSI, Pharmacist and Co-Founder of RoCa Healthcare.
Written in collaboration with Active Iron.

Constipation is one of the biggest reasons women stop taking iron supplements during pregnancy—but it doesn’t have to be. Here’s what every mum-to-be should know about iron, gut health and staying comfortable throughout pregnancy.

Let’s talk about iron. If you’re pregnant, you’ve probably already heard a hundred different things about it: take it on an empty stomach, take it with orange juice, it’ll wreak havoc on your gut, you can’t live without it. So, which bits are true?

Here’s the honest version: your iron needs go up a lot during pregnancy, and yes, iron supplements have a bit of a reputation for causing tummy trouble. That’s exactly why so many mums-to-be end up dreading their daily tablet, or quietly stop taking it altogether. We don’t want that to be your experience. So, let’s break down why iron actually matters, how much you need and—because gut health is at the heart of what we do at RoCa—how to keep things moving comfortably while you’re on it.

In this guide, we’re covering:

• How much iron you actually need in pregnancy
• Why it matters so much for you and baby
• The side effects nobody warns you about (constipation, we’re looking at you)
• What to think about when choosing a supplement
• A genuinely simple food trick that can help
• How SylliFlor can support your gut through pregnancy and beyond

How Much Iron Do You Need During Pregnancy?

Your iron needs increase during pregnancy to keep up with your growing baby and your own expanding blood volume—your body is doing a lot of work behind the scenes. According to HSE and NHS guidance, anaemia in pregnancy is generally diagnosed when haemoglobin (Hb) drops below 110 g/L in the first trimester, or below 105 g/L in the second or third.¹

Alongside haemoglobin levels, ferritin levels are a good indicator of depleted iron stores. The standard serum ferritin cut-off value used to diagnose iron deficiency during pregnancy is less than 30 µg/L.

If your levels come back low, your midwife, GP or obstetrician might recommend a daily iron supplement. These are usually best taken on an empty stomach or with a source of vitamin C, since vitamin C is recognised as helping your body absorb iron more effectively.² As always, follow whatever your own healthcare provider recommends for you. Everyone’s situation is a little different.

Why Does Iron Matter During Pregnancy?

Fair question. Iron has a genuinely important job to do. Under EU-authorised health claims, iron contributes to:³

• Formation of red blood cells and haemoglobin
• Oxygen transport
• Energy & Reduction of Tiredness & Fatigue
• Immunity
• Cognitive Function

In addition, low iron during pregnancy increases the risk of premature birth, low birth weight and severe maternal fatigue, as well as the chances of baby having low iron at birth.⁴

That’s why iron screening—and topping up when needed—is such a routine part of antenatal care. If you’re ever unsure about your own levels or what they mean for you, that’s a conversation for your midwife or doctor; they’ll have the full picture from your bloods and history.

The Not-So-Fun Part: Constipation

Here’s the bit nobody puts on the front of the box. The most common complaint with iron supplements, hands down, is constipation. Some people also notice:

• Bloating
• Nausea
• Dark stools
• The occasional bout of diarrhoea or stomach upset (less common, but it happens)

It’s genuinely one of the biggest reasons people stop taking their iron early or put off starting altogether. If side effects are hitting you hard, don’t just white-knuckle it—have a chat with your pharmacist or GP. There are different iron types and doses out there, and finding the right one for your body can make a real difference.

Picking the Right Supplement for You: Active Iron

Not all iron supplements are created equal. A lot of traditional oral iron supplements are poorly absorbed, and it is the unabsorbed iron that causes gut irritation that leads to common side effects such as constipation and nausea. Iron supplements come in different forms, different doses of elemental iron and are sometimes combined as part of a multivitamin. Some you can pick up over the counter; others come via prescription. Tolerance really is personal—what causes constipation for one person might sit perfectly well with someone else. Your pharmacist or GP is your best resource for weighing up the options against your own tolerance, needs and budget.

As a pharmacist, Active Iron is the one I reach for most often when patients tell me they’re worried about side effects. It’s formulated to be absorbed more effectively than standard ferrous sulfate,⁵ and it is clinically proven to increase iron levels whilst avoiding gut irritation, including nausea, constipation and more.⁶ It’s a great option to raise with your own pharmacist if constipation has been putting you off taking iron consistently.

Learn more about Active Iron

The Kiwi Trick 🥝

This one sounds almost too simple, but it’s worth knowing. I know an amazing midwife in Kilkenny who swears by both Active Iron and patients eating a kiwi fruit around 20–30 minutes before it. Kiwis are a source of soluble fibre and contain a natural enzyme called actinidin, which has been studied for its role in supporting digestive movement.⁷ They’re easy to digest and generally considered safe in pregnancy, though, as with anything new, flag it with your midwife or doctor if you’re ever unsure.

Supporting Gut Health During Pregnancy with SylliFlor

Psyllium husk is a well-recognised source of soluble fibre that contributes to normal bowel function as part of a varied, balanced diet. SylliFlor is a high-fibre, psyllium-based supplement that is great throughout pregnancy. Psyllium regulates the bowels, so you can increase or decrease it depending on your symptoms too.

When our community reaches for it:

• First trimester: to help keep things regular in those early, unpredictable weeks
• Second and third trimester: alongside iron supplementation, to help support normal bowel function
• Hospital bag: to support the first bowel movement postpartum
• Postpartum: to support digestive comfort while your body recovers and adjusts, especially through breastfeeding

For home use, explore the SylliFlor 200g tub. For convenient daily portions, see the SylliFlor sachets, or try the SylliFlor Travel Pack.

Pregnancy asks a lot of your body; the least we can do is make the gut part a bit easier. 💚 Active Iron and SylliFlor work together to help you keep feeling good while supporting your growing baby.

Real Reviews from Real Mums

Frequently Asked Questions

Can I take fibre supplements while pregnant?

Yes, SylliFlor is safe during pregnancy and breastfeeding. Always space iron and fibre apart, and it is recommended that you consult your healthcare provider when taking any supplements.

Can iron supplements make your stools black?

Yes. Dark stools are a common and generally harmless side effect of iron supplementation. Speak to your healthcare provider if you have concerns or notice anything unusual.

Can I take iron and psyllium together?

Yes, but leave approximately one hour before or two hours after taking your iron to help maximise absorption.

How long should I take iron after birth?

Doctors often recommend continuing iron for two to three months postpartum to rebuild your stores, especially if blood loss was significant during delivery. Follow the advice given by your own healthcare provider.

Can I use SylliFlor while breastfeeding?

Yes. Many new mums find it helpful for gentle, natural gut support during the recovery and breastfeeding stages.

About the Author

Róisín Cahill, MPSI

Róisín is a registered pharmacist and Co-Founder of RoCa Healthcare. She has a special interest in digestive health, women’s health and evidence-based nutritional care, helping both healthcare professionals and the public make informed decisions about gut health and supplementation.

This article was written in collaboration with Active Iron, whose clinically proven iron formulation has been developed to optimise iron absorption while being gentle on the stomach.

References

1. HSE, National Maternity Guidelines — Anaemia in Pregnancy screening thresholds.
2. European Commission / EFSA, EU Register of Nutrition and Health Claims, authorised claims for iron and vitamin C under Regulation (EC) No 1924/2006, as established by Commission Regulation (EU) No 432/2012.
3. EU Register of Nutrition and Health Claims — authorised claim for fibre sources contributing to normal bowel function, subject to product-specific conditions of use.
4. Elaine K. McCarthy et al., The American Journal of Clinical Nutrition (2024); NHS, vitamins, supplements and nutrition in pregnancy guidance.
5. Wang et al. (2017), Acta Haematologica, 138: 223–232.
6. Ledwidge, M. et al., PRECISION Study, International Journal of Clinical Pharmacy (2023).
7. Research on kiwifruit soluble fibre and actinidin content and their role in digestive comfort (general nutrition literature).