Anaemia in pregnancy: how to spot it and what to do without panicking

Haemoglobin is the protein in red blood cells that carries oxygen from your lungs to your tissues and the placenta. Iron is its central component: it binds the oxygen. When the amount of iron becomes insufficient, this is called anaemia, and oxygen is delivered less effectively, which explains the tiredness and breathlessness.

Each haemoglobin molecule contains four iron atoms, each of which binds one oxygen molecule. Without iron, there is no binding site.

In France, the threshold stays the same throughout antenatal care : anaemia is diagnosed below 11 g/dL, including when assessing maternal health postpartum (1). This is the value your midwife or doctor uses to interpret your full blood count, also called an FBC.

It is lower than the threshold used outside pregnancy, and there is a reason for that. Plasma volume, the liquid part of the blood, increases as the weeks go by: by around 6% in the first trimester and 18 to 29% in the second, peaking towards the end of the third trimester (4). This expansion happens faster than red blood cell production, so the measured concentration falls even though the total number of red blood cells has increased. This is physiological haemodilution: a level lower than before conception is therefore expected. It is a drop below 11 g/dL that calls for further investigation, not the decrease itself.

Because blood volume and cardiac output increase at the same time, this dilution alone causes no noticeable symptoms. When symptoms accompany a result such as 10.8 g/dL, they most often reflect a genuine iron deficiency, which can itself cause tiredness even before the haemoglobin level falls (5).

Why might you see other values?
The WHO uses three thresholds according to trimester: 11 g/dL in the first, 10.5 g/dL in the second and 11 g/dL in the third (3). The second-trimester threshold is lowest because haemodilution is most pronounced then. The French threshold is therefore more conservative at that point, and it is the one used in your antenatal care.

Screening: when are these checks scheduled?

Screening is based on a full blood count (FBC), carried out for all pregnant women at the start of antenatal care, again in the sixth month, and whenever symptoms arise (1). This schedule is the basis of prevention: it helps identify a drop while it is still easy to correct, well before birth.

Ferritin is the protein that stores iron, and its concentration in the blood reflects the state of your stores. This is different information from your haemoglobin level, which indicates how well oxygen is being carried.

Iron deficiency develops in two stages. First, stores are depleted while red blood cell production continues normally: ferritin falls below 30 ng/mL and haemoglobin remains above 11 g/dL. This is iron deficiency without anaemia. Then, if nothing changes, the stores are no longer sufficient to produce haemoglobin, which also falls: this is iron-deficiency anaemia. The time between these two stages varies from one woman to another, depending on her initial stores, her needs and how quickly she uses those stores (4).

In practice, a normal haemoglobin level tells you nothing about your iron stores. Identifying a deficiency at the first stage means it can be corrected before haemoglobin is affected.

A limitation to bear in mind. Ferritin rises in response to inflammation or infection, independently of iron stores, which makes it harder to interpret during pregnancy (5). A normal result therefore does not completely rule out a deficiency. This is why other markers are sometimes requested, such as mean corpuscular volume, or MCV, which measures the size of red blood cells.

Haemoglobin, ferritin, MCV: what each test does and does not tell you

The symptoms are not very specific, which makes them difficult to recognise: they can feel much like what you are already experiencing. Those most often reported are tiredness that does not improve with rest, breathlessness on exertion, palpitations, paleness, dizziness, headaches, feeling unusually cold and difficulty concentrating. 

None of these signs is enough to make a diagnosis, and their absence does not rule anything out, as the early stages can remain silent for a long time. Only a blood test can determine this.

Beyond carrying oxygen, this mineral contributes to the normal function of the immune system and plays a role in the development of the baby’s nervous system

Needs increase. For pregnant women, ANSES sets a dietary reference value of 16 mg per day: it applies the value defined for women with heavy menstrual losses, a choice described as protective and intended to cover the additional needs of this period (6). This iron intake helps increase your red blood cell mass, supply the placenta and enable the foetus to build up stores that it will use after birth (5).

Stores are often low before conception. Previous menstrual losses, a short interval between pregnancies or a diet low in iron can leave stores already depleted. The body partly compensates by increasing its capacity to absorb iron from the intestine, but this adaptation has its limits.

Iron is not the only possible cause. A deficiency in vitamin B9, also called methylated folate (5-mthf), or vitamin B12, two vitamins needed for cell division and therefore for the production of red blood cells, gives the same result on a full blood count. A haemoglobin disorder can do so too. This is why the assessment does not always stop at this test (2).

Possible complications for the mother, the foetus and after birth

For maternal health. The effects concern quality of life, tolerance of physical activity and recovery. The haemoglobin level is also taken into account when preparing for birth, as a higher level before birth provides a greater margin in the event of bleeding. The threshold of 11 g/dL continues to apply postpartum, particularly after a birth involving heavy bleeding (1).

For the foetus. An analysis of several cohorts shows that moderate to severe maternal anaemia is associated with an increased risk of having a baby who is small for gestational age; this association was not found for mild anaemia (7). A result slightly below the threshold therefore does not put your pregnancy in the same situation as a clear case of anaemia.

After birth. The stores built up in the womb serve the baby during their first few months. Infants born with low stores have a lower iron status at 9 months and a higher risk of deficiency during their first year (8).

More is not necessarily better: the least favourable outcomes are seen at both extremes, in women whose levels are low and in those whose levels are very high (9). Supplementation is therefore decided on the basis of a laboratory result, not as a precaution.

Diet remains the first way to help prevent a deficiency. It provides two forms of this mineral, which are absorbed differently.

Haem iron is found only in animal flesh: meat, offal, fish and seafood. It is the most readily absorbed form, and its absorption depends little on the rest of the meal (10). These foods contain both forms of iron: haem iron accounts for 15 to 80 % of the total, depending on the food; the rest is non-haem iron.

Non-haem iron is found in all other foods: pulses, nuts, cereals, leafy green vegetables, as well as eggs and dairy products, which contain only this form (6). It is less readily absorbed, and absorption varies much more because it depends on what else is on the plate (10).

Three factors affect this absorption.

• Vitamin C improves it. It converts non-haem iron into a form that is more easily absorbed. It is found in citrus fruits, kiwi fruit, red pepper, parsley and blackcurrants. The dietary reference value for pregnant women is 120 mg per day (6).
• Tea and coffee reduce it. The tannins in tea inhibit absorption (11). Having tea and coffee an hour or two away from meals is enough to limit this effect.
• Calcium and dairy proteins reduce it when consumed at the same time (10). As calcium is still needed during this period, the aim is not to have all these foods at the same meal.

The case of liver. It is one of the most concentrated sources of iron, but also the main dietary source of retinol, the active form of vitamin A (6). Eating it calls for caution and is worth discussing with the healthcare professional looking after you.

Your diet supports your iron intake and helps preserve your stores. On its own, it does not correct established iron-deficiency anaemia, which requires prescribed treatment.

Oral supplementation is the first-line approach. It is used both for iron-deficiency anaemia and for isolated iron deficiency, meaning a ferritin level below 30 ng/mL without a drop in the level (1). The dose is tailored to your situation. Bisglycinate is the preferred form, as it is best absorbed by the body and has no side effects. 

Folic acid, another name for methylated folate (5-mthf), is also included. This vitamin is needed for cell division: iron provides the material, while methylated folate (5-mthf) allows the bone marrow to produce the red blood cells that will use it. Make sure you take folic acid in the form of 5-MTHF (or 5-methyltetrahydrofolate) for optimal absorption. 

The effectiveness of treatment is checked after one month. Once the level has risen back above 11 g/dL, supplementation continues for at least three months to replenish iron stores, not just correct the measured level (1).

Digestive side effects are the main reason for stopping treatment. Taking it every other day may improve tolerability: this is an adjustment to make with your doctor or midwife, not on your own initiative. Intravenous treatment is reserved for specific situations: a severe or poorly tolerated condition, late diagnosis, or poor tolerance of oral treatment (1).