Blood disorders in pregnancy

Plasma volume increases by more during pregnancy than does red cell mass, leading to haemodilution and a fall in the haematocrit from about 40% to 33%, with a nadir usually reached at 24–32 weeks’ gestation. Anaemia during pregnancy is defined as a haemoglobin concentration of below 105 g/L during the second and third trimesters and below 110 g/L in the first trimester. The commonest haematological problem encountered in pregnancy is iron-deficiency anaemia. Routine iron supplementation in all pregnant women is probably not justified in developed countries, but if iron deficiency is detected it is advisable to treat as early as possible. Normal pregnancy is associated with marked changes in all aspects of haemostasis, the overall effect of which is to generate a state of hypercoagulability. These changes in haemostasis, while reducing the risks of excessive blood loss at delivery, significantly increase the risk of venous thromboembolic disease in pregnancy.