Anaemia is one of the things that most often shows up in your blood during pregnancy. I notice that many pregnant women get a fright when their Hb is a little lower, while a mild drop is actually normal. In this article I explain how that works and which values really matter.
Your blood volume rises considerably during pregnancy, so your Hb almost always dips a bit. Still, it is important to know when a low Hb points to a real iron shortage. Below you will read what Hb and ferritin show, which cut-off values apply per trimester and what you can do yourself.
Why is anaemia more common in pregnancy?
Anaemia is more common in pregnancy because your blood volume rises by about half. Your body makes more blood plasma than red blood cells, which dilutes the haemoglobin level. On top of that your baby needs a lot of iron, especially in the third trimester. That combination makes a low Hb very common.
This dilution is called physiological anaemia and is usually not a problem. The tricky part is that a real iron shortage looks roughly the same at first. That is why your midwife looks at more than just your Hb.
According to the World Health Organization a large share of pregnant women worldwide has anaemia. In the Netherlands that figure is lower, but it remains one of the reasons your Hb is checked as standard.
Which blood values: Hb and ferritin
The two most important values are haemoglobin (Hb) and ferritin. Your Hb shows how much oxygen your blood can carry and drops with anaemia. Your ferritin shows how large your iron stores are. Together they can indicate whether a low Hb is due to iron shortage.
Hb is the first value drawn, because it is quick and cheap. If your Hb is low, ferritin can help to work out whether iron shortage is involved. A low ferritin points to an empty iron store, sometimes before your Hb even drops.
Sometimes serum iron is also drawn, but that value swings a lot from day to day and says less on its own. Ferritin gives a more stable picture of your stores. Which values are useful for you is something you discuss with your midwife or GP.
What are the symptoms of anaemia in pregnancy?
Anaemia can cause fatigue, paleness, dizziness and shortness of breath on exertion. Headaches and heart palpitations also occur. The tricky part is that many of these complaints can simply belong to a pregnancy. That is why a blood value is more reliable than going by how you feel.
Mild anaemia often gives no complaints at all. Some women only notice something once the Hb has dropped considerably. According to Thuisarts.nl the complaints usually go away again once an iron shortage is topped up.
If you have complaints that worry you, always discuss them with your midwife or GP.
Which Hb value is too low per trimester?
The threshold for anaemia differs per trimester, because your Hb naturally falls as your blood volume rises. The World Health Organization uses a Hb below 110 grams per litre in the first and third trimester, and below 105 in the second. The table below lists the cut-off values.
| Trimester | Hb cut-off (WHO) | What it can mean |
|---|---|---|
| First trimester | Hb < 110 g/l | Possible anaemia, often from dilution or iron shortage |
| Second trimester | Hb < 105 g/l | The threshold is lower due to the sharply risen blood volume |
| Third trimester | Hb < 110 g/l | Possible anaemia, your iron need is highest then |
| Ferritin (iron stores) | Often < 30 µg/l as a signal | Points to a low or empty iron store |
These values are guidelines, not hard limits. Laboratories and guidelines may use slightly different cut-off values, and your midwife always weighs your whole situation. A result just under or over a threshold says little on its own.
Iron through food and supplements
You can support your iron intake through your food and, if needed, through supplements. The Voedingscentrum names meat, wholegrain products, pulses and green leafy vegetables as good iron sources. Vitamin C can help your body absorb plant-based iron better. Supplements you only use on advice.
Iron from animal products is absorbed more easily by your body than iron from plants. So combine plant-based sources with some vitamin C, for example a piece of fruit. Coffee and tea with a meal can slow absorption down.
Do not take iron tablets on your own initiative, because too much iron is not without risk. Whether a supplement is useful depends on your Hb and ferritin. You decide that together with your midwife or GP.
Testing your own iron
The standard Hb testing runs through your midwife. If you also want to map your iron status yourself, for example before you get pregnant or between check-ups, you can do so at Lunara without a referral. The Iron Status test looks at values like Hb, ferritin and iron.
Such a test can be handy if you are often tired or had an iron shortage before. This belongs in the broader series on blood testing during pregnancy, in which we also cover your blood group and other values. For the blood group itself, read our article on blood group and rhesus factor.
Important: testing yourself does not replace the regular pregnancy check-ups. You always discuss an abnormal result with your midwife or GP.
Frequently asked questions
Is a low Hb in pregnancy dangerous?
A mildly lowered Hb is very common and usually harmless, because your blood is diluted. With a more strongly lowered Hb your midwife may advise iron. Always discuss a low result with your midwife or GP.
What is the difference between Hb and ferritin?
Hb shows how much oxygen your blood can carry right now. Ferritin shows how large your iron store is. Your ferritin can be low before your Hb drops, so together they give a fuller picture.
Can I prevent anaemia with food?
An iron-rich diet can help, but gives no guarantee, because your iron need rises sharply in pregnancy. The Voedingscentrum advises eating varied with iron-rich products. Whether a supplement is needed depends on your blood values.
When is my Hb drawn during pregnancy?
Usually at the first check-up and again around week 27. At those moments the chance of anaemia is greatest. With complaints your midwife may draw blood more often.
If I could give you one thing to take away: do not get an immediate fright from a slightly lower Hb, but do not take it too lightly either. The combination of Hb and ferritin tells you more than a single value. Discuss your results calmly with your midwife, so you know where you stand.
References
- World Health Organization (WHO). Haemoglobin concentrations for the diagnosis of anaemia and assessment of severity. WHO, 2011.
- NHG and Thuisarts.nl. Anaemia (bloedarmoede). Dutch College of General Practitioners.
- Voedingscentrum. Iron in the diet. Voedingscentrum.
- RIVM. Pregnancy and nutrition. National Institute for Public Health and the Environment.
Every blood test result through Lunara includes a professional assessment by a BIG-registered doctor. Blood testing through Lunara does not replace the regular pregnancy check-ups. For treatment decisions, discuss your results with your GP or midwife.
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