Wed3November0832PM 2

A 27-year-old parturient at 37-weeks gestation is admitted to the labour ward. She has had an asymptomatic antenatal period.

The following haematological values are available:

Hb 10.5 g/L (115-165)

Platelets 200 ×109/L (150-400)

MCV 70 fL (80-96)

Which of the following is the most likely cause?

(Please select 1 option)

Folate deficiency

Pre-eclampsia

Haemolysis

Sickle cell disease

Iron deficiency Correct

Explanation

The limited haematological picture of this patient is one of a mild normocytic anaemia and normal platelet count.

The commonest cause of anaemia during pregnancy is iron deficiency. It can occur in 75-95% of patients. Anaemia is defined as a haemoglobin of less than 110 g/L in the first trimester and <105 g/L in the second and third trimesters. In addition to a low haemoglobin, typically there will be a low mean cell volume (MCV), mean cell haemoglobin (MCH) and mean cell haemoglobin concentration (MCHC). For mild cases of iron or coexisting vitamin B12 and folate deficiency, the MCV may be normal.

Further tests are required to establish iron deficiency. These include a low serum ferritin (<15 µg/L) and less reliable indices such as serum iron and total iron binding capacity.

Iron deficiency in pregnancy results from a number of factors, these are:

Insufficient dietary iron to meet the nutritional needs of the mother and fetus

Multiple pregnancy

Blood loss, and

Reduced iron absorption from the gut.

During pregnancy the plasma volume increases by approximately 50%, but red blood cell (RBC) mass increases by only 30%. This situation results in a dilutional anemia. The RBC mass increases linearly from the first trimester to delivery and the plasma volume plateaus or stabilises or falls slightly near term (due to an increase in atrial natriuretic peptide). Therefore haemoglobin concentrations are lowest between 28 and 34 weeks' gestation.

A less common anaemia in pregnancy is vitamin B12 and folate deficiency. The normal MCV might preclude the diagnosis.

The platelet count does decrease during pregnancy, particularly in the third trimester. This is termed as "gestational thrombocytopenia". It is partly due to haemodilution and partly due to increased platelet activation and accelerated clearance. Thrombocytopenia typically occurs in pre-eclampsia and HELLP syndrome. Pre-eclampsia per se is not a primary cause of anaemia.

A typical blood picture of a haemoglobinopathy such as sickle cell disease results in quantitative and qualitative defects, the former resulting in a severe anaemia exacerbated by haemodilution and factors that contribute towards iron deficiency. The cells are typically microcytic.

Haemolysis is a possible cause but unlikely.

Answer Statistics

1

4%

2

56%

3

42%

Times answered: 275