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