The haematological system undergoes significant changes during pregnancy. A knowledge of these changes is essential to enable clinicians to determine what is within normal parameters and what is pathological. The recognized haematological changes during pregnancy are detailed in Chapter 1.
Anaemia of pregnancy
A measure of haemoglobin (Hb) levels should be made at booking and at 28 weeks’ gestation.
Anaemia during pregnancy may result from dilutional physiological changes, iron deficiency, folate deficiency, new-onset pernicious anaemia, or pre-existing diseases, including haemoglobinopathies or hereditary spherocytosis. Establishing the cause is paramount and early treatment will minimize the harmful effects.
The 2011 UK guidelines for the management of iron deficiency in pregnancy defined anaemia as:
• <110 g/L in the first trimester
• <105 g/L in the second and third trimesters
• <100 g/L postpartum.
Anaemia impairs oxygen delivery and results in an increase in cardiac output and oxygen demand, with a loss of functional reserve and an increased risk of maternal and fetal ischaemia. Remember, blood loss is expected at an uncomplicated normal delivery (500 mL) and at caesarean section (1000 mL).
Iron deficiency is the leading cause of anaemia; this may be due to pre-existing low iron levels secondary to menorrhagia, inadequate diet, pregnancy within the last year or due to increased iron demands (such as multiple pregnancy). It is associated with low birth weight, preterm delivery and increased blood loss at delivery.
Iron deficiency can be diagnosed using serum ferritin and total iron binding capacity saturation more reliably than mean corpuscular volume or mean corpuscular haemoglobin concentration. Without the presence of inflammatory disease, serum ferritin is the best indicator of iron stores in pregnancy. The 2011 UK guidelines for the management of iron deficiency in pregnancy advise iron replacement therapy for women with serum ferritin levels less than 30 µg/L, as this represents early iron depletion that will deteriorate with increasing gestation. A serum ferritin <15 µg/L is diagnostic of iron deficiency. Treatment is with 100–200 mg elemental iron per day. Inhibitors to iron uptake in the intestine, such as phytic acid and tannins, should be avoided. Parenteral iron may be indicated when oral therapy is not tolerated, absorbed or compliance is in doubt. The World Health Organization (WHO) recommends iron supplementation for all women. However, analysis of studies in the Cochrane database have not provided sufficient evidence to support this.