Overview

Low iron levels, also known as anaemia, are a common issue that can develop during pregnancy. There are a variety of ways of improving your iron levels, ranging from simple changes to your diet to medical replacement therapies. Some of the most frequently prescribed medications can have side effects, with constipation being one of the most common. If you have experienced, or are worried about experiencing such side effects, we will discuss alternatives that may be less likely to cause constipation.

Understanding iron and its role in pregnancy

What is iron?

Iron is an essential nutrient that your body uses every day for a wide variety of essential functions. It is found in a wide range of dietary sources, including red meats, leafy greens, shellfish and nuts.¹ The most common causes of low levels of iron (an iron deficiency anaemia) are due to dietary causes, although sometimes there can be underlying problems with gut absorption that are responsible.

What is the role of iron in the body?

Iron is typically found as part of a complex protein called haemoglobin, which sits inside the red blood cells of the bloodstream.² The haemoglobin compound is responsible for transporting oxygen around your body, which allows your body to make enough energy to keep you healthy.

Why does anaemia develop in pregnancy?

Your body will undergo many changes during pregnancy, which often start to occur within a few weeks of conception. The body increases the levels of red blood cells (and subsequently haemoglobin) by approximately 20-30%, although the amount of fluid in the bloodstream increases even more, with some estimates of around 30-50%.³ This relative mismatch results in the haemoglobin getting ‘diluted’, which means that pregnant women appear slightly more ‘anaemic’ on blood tests than the general population, despite actually having more haemoglobin in their bloodstream than the average person. However, as levels appear lower, clinicians will generally recommend iron supplementation if there are any concerns about below-average iron levels in the blood.

What are the risks of iron deficiency in pregnancy?

Iron is important in delivering oxygen to cells around the body, which is used for energy. Without this, you will start to feel tired. In addition to the usual risks of anaemia, in pregnancy specifically, less mobility from fatigue can increase the risk of blood clots. Anaemia can also affect your baby’s growth and birth weight, in extreme cases resulting in preterm birth and impaired brain development in the womb.^4,5 If not recognised and treated, such issues can cause lifelong disability.

Another consideration is planning ahead for the birth of your baby, as labour can sometimes be complicated by a larger than expected blood loss. Although the body has made many changes in pregnancy, if your iron levels are already low before labour, you may feel the effects of heavy blood loss more significantly. Adequate replacement of low levels in pregnancy will not prevent haemorrhage but may lessen the risk.

Should I take an iron supplement if I am pregnant, even if I have no symptoms?

Most healthcare groups will recommend taking a pregnancy multivitamin. These supplements contain a wide variety of helpful substances, including low doses of iron. Not every woman needs to be on high-dose iron supplements, but if your levels remain low despite taking a multivitamin your healthcare provider may recommend taking a higher dose.

How do I know that I might need iron replacement?

Common signs that you are suffering from iron-deficiency anaemia, and may need iron replacement, can include:⁶

• Feeling tired all the time
• Shortness of breath
• Dizziness, especially if sitting or lying down
• Palpitations (fluttering sensations in the chest)
• ‘Brain fog’, or issues with memory

Some of these symptoms, including mild breathlessness, maybe a side effect of pregnancy rather than true iron deficiency. There are other causes of anaemia, but these result from deficiencies other than iron, such as low vitamin B12 and folate levels.

Why do traditional iron supplements cause constipation?

Oral iron tablets — such as ferrous sulphate, the most common form — are swallowed, transported into your stomach and then pass into your intestines. During this process, they are gradually absorbed. There are several proteins in the gut walls that pick up the iron, but this is limited so that only a limited amount of iron is picked up at a time. Any remaining iron is then eventually removed from the body as stool.

Mechanism of constipation with Iron

The exact reason why iron supplements cause constipation is unclear, however, some researchers are of the opinion that as the iron is transported out of the gut and into the bloodstream, water is drawn along with it.⁷ This causes the material left behind – which becomes stool – to be very dry, and harder for the body to remove.

Am I guaranteed to be constipated if I take iron tablets?

Everyone is different, and many people will be able to tolerate tablets without issues. It is important to remember many factors can worsen constipation, and it is worth addressing these before changing the preparation of iron tablets.

Factors that worsen constipation

Your body is regulated by hormones, chemicals released from one part of the body that can affect how the whole body works. During pregnancy, the hormone progesterone is responsible for many of these changes. Progesterone can affect gut motility,⁸ meaning it slows the movement of stomach contents through the intestines. This naturally leads to slower bowel movements, and can cause constipation on its own, which may be further worsened by the side effects of medications such as iron supplements. Although the effects of pregnancy hormones cannot be controlled, many modifiable factors can increase the risk of constipation.

Do I need to worry about constipation in pregnancy?

Constipation is very common during pregnancy, with nearly 1 in 4 patients reporting experiencing this at some point in their pregnancy.⁹ Although unpleasant, it is unlikely to cause long-term harm. It is worth noting that long-term constipation-related straining may lead to the development of other issues such as haemorrhoids, anal fissures and rectal prolapse.¹⁰

What other treatment options are available?

Make simple dietary changes

• Increase iron-rich foods – Incorporate sources such as lean meats, leafy greens, and legumes
• Consume high-fibre foods – Whole grains, fruits, and vegetables help prevent constipation
• Boost vitamin C intake – Foods like citrus fruits, berries, and tomatoes can improve iron absorption
• Limit caffeine – Caffeine can adversely affect the bowels, and worsen iron absorption¹¹

Stay hydrated

If you do not drink enough water over the course of the day, your body will try to hold onto water in whatever way it can. This can make your stool dry and firm, which will make constipation worse. The average woman should aim to drink around 2-2.5 litres of water per day, but if you have blood pressure issues or kidney problems, you should discuss daily fluid limits with your doctor first.

Engage in regular physical activity

Constipation is made worse by being sedentary. Any effort to increase your activity levels, no matter how small, can help improve your symptoms:

• Gentle exercise
• Prenatal yoga classes
• Swimming 

Consider alternative iron supplements

The following options represent pregnancy-safe alternatives to iron replacement with ferrous sulphate. Many of these alternatives come with their own form of side effects and can be significantly more expensive than standard iron tablets. Please remember to always discuss with your healthcare provider before starting a new therapy.

Ferrous bisglycinate chelate

This is a synthetically produced form of iron, associated with fewer side effects than standard iron tablets.¹²

Haem iron

Haem is a naturally-occurring iron that is only found in animal sources (such as meat) and has fewer side effects but has to be consumed in large amounts to be a useful replacement. Best used alongside other iron replacement methods.¹³

Polysaccharide-iron complex

This is available as both sugar-coated tablets and sugar solutions, mostly used in children. Takes a long time to work, and can cause similar symptoms,especially inliquid form.¹⁴

Intravenous iron replacement

This involves the injection of iron over 15-30 minutes. This can avoid the constipation risks, but carries other significant risks including allergic reaction, and should only be administered by and with the approval of a trained professional.¹⁵

How to choose the right non-constipating prenatal iron supplement

The typical amount of iron needed during pregnancy is approximately 7mg per day.¹⁶ For some, it will be enough to get these iron stores from the diet advised above, but if you need an alternative iron preparation, please obtain this from a registered prescriber. Although these preparations may improve constipation, they can have other side effects such as nausea, vomiting and heartburn that can be more problematic.

Summary

Iron deficiency anaemia is a common issue during pregnancy. There are a wide variety of methods to manage this, though certain medicinal forms of iron replacement can cause side effects. The most common side effect of iron tablets is constipation, which can be worsened by the natural changes in pregnancy. Not everyone will suffer from this, but if you are struggling with constipation caused by ferrous sulphate tablets, you can consider trying to focus on an iron-rich and high-fibre diet, staying well hydrated, avoiding caffeine, and using alternative medical preparations. If you cannot tolerate the oral iron tablets, a discussion can be had with your healthcare provider about alternative methods of iron administration, such as intravenous infusions, although you should be aware these have their own list of risks and side effects.