The circulating red cell mass increases by 20-30% during pregnancy, with rises in both cell number and size. It rises more in women with multiple pregnancies, and substantially more with iron supplementation (~29% compared with 17%). Serum iron concentration falls, the absorption of iron from the gut rises and iron-binding capacity rises in a normal pregnancy, since there is increased synthesis of the f 1-globulin, transferrin. Plasma folate concentration halves by term, because of greater renal clearance, although red cell folate concentrations fall less. Even now, only ~20% of fertile women in the UK have adequate iron reserves for a pregnancy and ~40% have virtually no iron stores. Even relatively mild maternal anaemia is associated with increased placental:birthweight ratios and decreased birthweight. However, inappropriate supplementation can itself be associated with pregnancy problems . Erythropoietin rises in pregnancy, more if iron supplementation is not taken (55% compared with 25%) but the changes in red cell mass antedate this; human placental lactogen may stimulate haematopoiesis.
Pro rata, the plasma volume increases more than the red cell mass, which leads to a fall in the various concentration measures which include the plasma volume, such as the haematocrit, the haemoglobin concentration and the red cell count. The fall in packed cell volume from ~36% in early pregnancy to ~32% in the third trimester is a sign of normal plasma volume expansion.
The total white cell count rises, mainly because of increased polymorphonuclear leucocytes. Neutrophil numbers rise with oestrogen concentrations and peak at ~33 weeks stabilizing after that until labour and the early puerperium, when they rise sharply. Their phagocytic function increases during gestation. T and B lymphocyte counts do not change but their function is suppressed, making pregnant women more susceptible to viral infections, malaria and leprosy. The uterine natural killer cells express receptors that recognize the otherwise anomalous combination of human lymphocyte antigens (HLA-C, -E and -G) expressed by the invasive cytotrophoblasts. This is likely to be central to the maternal recognition of the conceptus .
Platelet count and platelet volume are largely unchanged in most pregnant women, although their survival is reduced. Platelet reactivity is increased in the second and third trimesters and does not return to normal until ~12 weeks after delivery.
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Once your pregnancy is over and done with, your baby is happily in your arms, and youre headed back home from the hospital, youll begin to realize that things have only just begun. Over the next few days, weeks, and months, youre going to increasingly notice that your entire life has changed in more ways than you could ever imagine.