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Blood disorders specific to pregnancy 

Blood disorders specific to pregnancy

Blood disorders specific to pregnancy

David J. Perry

and Katharine Lowndes


July 30, 2015: This chapter has been re-evaluated and remains up-to-date. No changes have been necessary.

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date: 25 April 2017

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 the nadir usually reached at 24 to 32 weeks gestation. Anaemia during pregnancy is defined as a haemoglobin concentration of <10.5 g/dl during the second and third trimesters.

Anaemias and haemoglobinopathies

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.

Folic acid—the requirement for folic acid doubles in pregnancy and dietary folate deficiency is the most frequent cause of gestational megaloblastic anaemia. This can be prevented by supplementation with 300 μ‎g folic acid daily, although higher doses of folate (up to 5 mg daily) are recommended to prevent neural tube defects.

Haemoglobinopathies—the diagnosis of variant haemoglobins and the thalassaemia syndromes before pregnancy or early in gestation is important. Screening is usually performed on a blood sample taken at booking. If a haemoglobin variant or thalassaemic indices are detected, then the partner should be tested to determine the risk of having an affected fetus and allowing informed prenatal counselling.

Haemostatic disorders

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, whilst reducing the risks of excessive blood loss at delivery, significantly increase the risk of venous thromboembolic disease in pregnancy (see Chapter 14.7).

Gestational thrombocytopenia—seen in about 8% of all pregnancies and accounts for more than 70% of cases of thrombocytopenia in pregnancy: its main differential diagnosis is immune thrombocytopenic purpura.

Disseminated intravascular coagulation—can be caused by intrauterine death with a retained fetus, severe pre-eclampsia, premature separation of the placenta (placental abruption), retained placenta, amniotic fluid embolism, haemorrhagic shock and transfusion reaction.

Inherited haemostatic disorders, e.g. haemophilia, von Willebrands disease—women with these conditions require specialist management during pregnancy.

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