The following haematological changes occur during pregnancy:

• 40-50% increase in plasma volume, reaching its maximum by week 32 of gestation, with similar increase in cardiac output

• Increase in red cell volume by approximately 18-25%, though more slowly than the increase in plasma volume

• Natural reduction in haemoglobin concentration: normal or elevated haemoglobin may signify pre-eclampsia in which plasma volume is reduced

• Increased iron requirement, particularly in last trimester

• Increases in platelet activation and levels of coagulation factors, particularly fibrinogen, Factor VIII and Factor IX

• Fibrinolytic system is suppressed

• Increased susceptibility to thromboembolism.

Blood loss during delivery

• About 200 ml of blood during normal vaginal delivery
• Up to 500 ml during Caesarean section.

This blood loss rarely necessitates transfusion provided that the maternal haemoglobin is above 10.0-11.0 g/dl before delivery.

Further investigation is needed if haemoglobin concentration does not return to normal by 8 weeks postpartum