Oxford Handbook of Midwifery by Janet Medforth, Sue Battersby, Maggie Evans, Beverley Marsh, Angela Walker

complex molecule with the ability to absorb oxygen easily and reversibly. The molecule is composed of iron and protein. The protein structure is inherited and is the part affected in haemoglobino- pathies, being either abnormal or partly missing.
A normal red blood cell (RBC) in an adult is filled with adult haemoglobin. Everyone inherits their haemoglobin type from their parents, half the responsible gene copies from each, and the usual type is HbAA.
Sickle cell trait
Sickle haemoglobin (abbreviated HbS) has an abnormality of the protein part of the molecule.
An individual inheriting HbS from one parent and HbA from the other will have haemoglobin type HbSA.
This is known as the sickle-cell trait.
The RBCs of such individuals will function normally and they will have few, if any, symptoms.
• However, these individuals have a 50% chance of passing this type of haemoglobin on to their children.
This condition confers immunity from the malaria parasite, which explains the prevalence of the condition in areas where malaria infection is endemic.
Due to population movement, individuals can inherit this type of haemoglobin even if their ancestry is from malaria-free areas.
Sickle cell anaemia
In this case, the individual inherits HbS from both parents, so the haemoglobin type is HbSS.
RBCs containing only HbSS react to hypoxia, acidosis, or dehydration by changing shape, from the usual bi-concave disc to a crescent or sickle shape.
These RBCs are more fragile, easily damaged, and will clump together, blocking capillaries.
Painful crises are provoked by the blockage of small blood vessels.
The overall effect is that the RBCs are haemolysed, rapidly causing chronic haemolytic anaemia.
Effects on childbearing
Subfertility
Impaired placental function
Increased risk of pregnancy-induced hypertension
Pulmonary and renal problems
Phlebitis
Women with this type of anaemia need to be well hydrated during labour and need careful monitoring to avoid hypoxia should an anaesthetic be required.
SICKLE CELL ANAEMIA
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Screening
Information about screening for sickle cell diseases and thalassaemias, including carrier status and the implications of these, should be given to pregnant women at the first contact with a healthcare professional.
Screening for sickle cell diseases and thalassaemias should be offered to all women as early as possible in pregnancy (ideally by 10 weeks). The type of screening depends upon the prevalence and can be carried out in either primary or secondary care.
Further reading

National Institute for Health and Clinical Excellence (2008). Antenatal care: Routine care for the healthy pregnant mother. Clinical guideline 62. London: NICE. Available at: M www.nice.org. uk/cg62.
CHAPTER 4 Antenatal care
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Thalassaemia
In this recessively inherited condition part of the haemoglobin protein is missing. The protein is made from structures called A and B chains. As several genes are responsible for the structure of these chains, it is pos- sible to have varying degrees of the condition.
B -thalassaemia minor
The individual inherits one normal gene from one parent and one affected gene from the other parent. This is a carrier state, and has little effect on health other than mild anaemia. Affected individuals can pass on the defective gene to their children.
B -thalassaemia major
The individual inherits defective genes from both parents and can make no, or very few, B chains, so does not produce sufficient haemoglobin. This results in severe anaemia requiring regular blood transfusions and therapy to remove excess iron from the blood.
A -thalassaemia
People with normal haemoglobin carry four A globin genes, two from each parent. A-thalassaemia results from the deletion of one or more of these genes. Table 4.2 shows the result of deletions of one or more of the genes and the effect on the type of haemoglobin produced.

Table 4.2 Effect of gene deletions
Gene deletions
Diagnosis
Adult blood
( aa/ – a )
 2