Haemoglobin (Hb) is the oxygen-carrying component of red blood-cells. Its normal range is around 12-16 g/dl. In pregnancy, many experts agree that the normal range can and should be extended to be 11-16 g/dl. When the level of this component falls below 11 g/dl, that is anaemia.
The short form 'Hb' is almost universally used to describe haemoglobin. So, if you encounter a tired junior doctor and he blurts out that, "You have a low Hb," what the poor chap means is that you are anaemic.
The abbreviation "g/dl" that appears in front of the numbers is the form of measurement used for the haemoglobin level. It simply stands for grams per decilitre.
What causes anaemia in pregnancy?
The production of haemoglobin and that of red blood cells (the latter by the bone marrow) is dependent upon the adequate supply of several "raw materials". The most important of these is iron.
Over 90 per cent of those found to have anaemia in pregnancy will have the problem because of iron deficiency.
What are the other possible causes of anaemia in pregnancy?
Vitamin B12 and/or folic acid deficiency could lead to anaemia. They are a relatively uncommon cause in pregnancy but, when evidence of iron deficiency is lacking, these possible causes need to be investigated.
Are there any other causes?
There are conditions which are collectively called "haemoglobinopathies". Affected people tend to have chronic anaemia and pregnancy will tend to make this worse. The most common among these are sickle cell disease and thalassaemia. These conditions are discussed in detail in Chapter 10, "Thalassaemia and sickle cell disease".
Iron deficiency is hardly ever a cause of anaemia in these conditions. In fact, the tendency is to have iron overload. This is a direct result of multiple repeated transfusions, which are inevitable in most of these conditions. The transfusions will have started in childhood. These conditions are hereditary.
Why does pregnancy make a woman prone to anaemia?
The demand for iron goes up quite markedly in pregnancy. This is because there is an expansion of the blood volume to meet the new demands of pregnancy. The red cell mass may go up by as much as 25 per cent. In addition to this, the fetus also takes its share. The fetus is totally dependent on the mother for everything, including iron.
The requirements for iron that is absorbed from the diet roughly doubles in pregnancy. In fact, the more advanced the pregnancy gets, the higher the requirements for iron. If the diet has poor iron supplies, the iron stores in the body will be mobilized but will not be adequately replenished from the diet. Eventually, the stores run empty and the haemoglobin levels start to fall. Some people conceive while already mildly anaemic, with hardly any iron stores. Such mothers will quickly become anaemic relatively early in pregnancy.
Without remedial action, the degree of anaemia continues to worsen with advancing pregnancy. The fetus will continue to extract all its required quantities from an already deficient mother and the Hb level gallops along downwards.
What sort of diet will be unfavourable for supplying dietary iron?
Vegetarians are at a particular disadvantage in this regard. This is simply because they don't get the so-called "heme" iron which is found in meat and other animal products only. "Heme" iron is much more easily absorbed and actually promotes absorption of non-heme iron as well from the gut. Vegans are therefore at a double disadvantage in this regard. They don't get to eat products with heme iron and the iron they get from plant products is not so efficiently absorbed.