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P.610 top paragraph:"A healthy woman bearing a normal sized fetus, with an average birth weight of about 3.3 kg, will increase her plasma volume by an average of about 1250 ml, a little under 50% of the average non-pregnant volume for white European women of about 2600 ml. There is little increase during the first trimester, followed by a progressive rise to a maximum at about 34-36 weeks, after which little or no further increase occurs. It seems certain that the frequently observed fall in plasma volume in the last six weeks of pregnancy is an artefact of measurement due to poor mixing of tracer when the woman lies supine and obstructs the circulation to her lower limbs. The maximum increase depends largely on the size of the conceptus. It is somewhat increased, perhaps to a mean of 1300 ml, in association with the bigger baby of multiparae and increases still more with twins, triplets and quadruplets." |