Blood and Neoplastic Diseases. Pregnancy Anaemia

Abstract

During normal pregnancy there is a fall in haemoglobin concentration which is often referred to as “the physiological anaemia of pregnancy.” This occurs because the red cell volume expands by at least 18% (reaching a maximum at term) but the plasma volume expands much more (by about half, reaching a plateau at around 34 weeks in the primigravida, but continuing to rise until term in the multigravida). Thus, though the total amount of haemoglobin in the body rises by 85g or so, its concentration drops by 1–2 g/ml. This fall in haemoglobin concentration is associated with a reduced arteriovenous oxygen difference, confirming that the increased oxygen requirements of pregnancy can readily be met. The disproportionate increase in the plasma volume is appropriate to the increased renal blood flow, which helps to eliminate the waste products of increased metabolism, and to the increased blood flow to the skin which is required to lose the excessive heat produced. Hence the fall in haemoglobin concentration does not signify “anaemia”: it is a normal physiological event and does not require treatment. © 1974, British Medical Journal Publishing Group. All rights reserved.