Anaemia is a common occurrence in pregnancy that is multifactorial. The term “anaemia” refers to a low concentration of haemoglobin within the blood. This means that there is inadequate transportation of oxygen around the body by red blood cells.
Pathophysiology
In pregnancy, the blood volume increases by approximately 1.2 - 1.5 litres. This is a physiological response that occurs in order to:
- Meet the increased demands of the maternal organs (placenta, uterus, breast, skin and kidneys).
- Meet the new demands by the growing foetus.
- Prepare the mother for the anticipated losses that occur during labour.
It is able to expand due to fluid retention (via the renin-angiotensin-aldosterone system) as well as an increase in the total number of red blood cells. However, the ratio at which the plasma expands compared to erythrocyte expansion is higher. This ultimately leads to haemodilution with the concentration of erythrocytes decreasing overall → anaemia.
These changes occur throughout pregnancy, beginning from the first trimester and most prominently in the second trimester (while being maintained throughout the third trimester). After labour there is an expected amount of blood loss as well. As a result the reference ranges for normal haemoglobin concentrations also differ throughout pregnancy. Let’s take a look at the table to see what the thresholds for Hb levels are throughout pregnancy:
Scenario | Hb level (g/L) |
Non-pregnant women aged ≥15 years old | 120 |
First trimester | 110 |
Second/third trimester | 105 |
Postpartum | 100 |
The most common cause of anaemia in pregnancy is iron deficiency, however, it may also be due to folate deficiency or vitamin B12 deficiency. Both folate and B12 are used in the development of the foetus, in particular with development of the neural tube.
⚠️ Risk factors
- Multiple pregnancies
- Hyperemesis gravidarum
- Vegeterian/vegan diet
- Iron deficiency anaemia prior to pregnancy
- Teenage pregnancy
- Short interval between successive pregnancies
😷 Presentation
The presenting features are similar to that of anaemia outside of the pregnancy period. It is often asymptomatic, but if the mother is symptomatic some of the features she may present with include:
- Lethargy and fatigue
- Shortness of breath
- Pallor
- Dizziness
- Cold peripheries
- Headaches
🔍 Investigations
An FBC is conducted at the first antenatal appointment/booking appointment (around 10 weeks) as well as at 28 weeks (beginning of third trimester). As mentioned earlier, the cause of anaemia needs to be identified and therefore it is not only important to look at the haemoglobin concentration but also at the mean cell volume (MCV).
- Low MCV → iron deficiency
- Normal MCV → haemodilution
- Raised MCV → vitamin B12/folate deficiency
Another thing that is assessed at the booking appointment is haemoglobinopathy screening (looking for thalassaemia in particular, as well as sickle cell disease in women who are at high risk of being a carrier).
Serum ferritin may be useful in the first trimester but is not
🧰 Managementx
The management once again is dependent on the type of anaemia present.
- Iron deficiency anaemia → oral ferrous sulphate. This should be continued until 3 months after the IDA has been corrected (to ensure stores are replenished).
- Folate deficiency → all women are advised to take 400mcg folic acid daily from pre-conception → 12th week of pregnancy. If at high risk then this should be increased to 5mg daily.
- Vitamin B12 deficiency → there are no guidelines on what form and dosage of B12 is recommended, however, it is typically IM hydroxycobalamin that is recommended by the BNF.
🚨 Complications
- Growth retardation
- Preterm birth
- Low birth weight
- Delayed postpartum recovery