Physiological adaptation to pregnancy – Hematology System
Blood is a tissue in the form of a liquid consisting of two major parts, the blood plasma, and the corpuscular part. In another sense, hematology is also known as a branch of medicine concerning blood cells, blood-forming organs, and abnormalities associated with cells and blood-forming organs. Pregnant women experience various anatomical, physiological and biochemical changes in the body. Most of these changes have occurred immediately after fertilization and continue throughout the pregnancy. Most of these changes are a form of body adaptation to the presence of the fetus. One of the important changes that occur is hematological changes. It occurs for preparing the body of pregnant women as a medium for fetal growth and development. The hematological changes in form of increased blood volume, hemoglobin concentration and hematocrit, immunological functions and coagulation factors.
Maternal blood volume began to increase early in pregnancy as a result of changes in osmoregulation and the renin-angiotensin system. This later results in sodium retention and an increase in total body water to 8.5 L. During that time, blood volume increased to 45% where the volume of red blood cells only increased up to 30%. This difference in increase can lead to “physiological anemia” in pregnancies with hemoglobin averaging 11.6 g / dl and hematocrit 35.5%. However, oxygen transport is not disturbed by this relative anemia, because the mother’s body compensates increasing cardiac output, increasing PaO2 and shifting right from the oxyhemoglobin dissociation curve. Pregnancy is often associated with a hypercoagulable state that provides benefits in limiting the occurrence of blood loss during labor. Fibrinolysis can quickly be observed later in the third trimester. As an effect of anemia, delusions, leukocytosis, and a decrease in platelet count by as much as 10% may occur during the third trimester. Because the needs of the fetus, folate, and iron deficiency anemia may occur if supplementation of these nutrients is not fulfilled.
- Blood volume
In pregnant women, there will be a significant increase in blood volume even though the increase varies for each woman. Increased blood volume starts in the first trimester of pregnancy. This will develop progressively from the 6th – 8th week of pregnancy and reaches its high position in the 32nd – 34th week of pregnancy. Later it will return to its original condition 2-6 weeks after delivery. The blood volume consists of blood plasma and blood components.
Early in the pregnancy, the volume of blood plasma will increase rapidly by 40-45%. This is influenced by the action of progesterone and estrogen in the kidney. Scientifically it is initiated by the renin-angiotensin and aldosterone pathways. Besides increasing plasma volume, there is also an increase in the volume of blood components, erythrocytes. The increased number of erythropoietin in pregnant women causes an increase in erythrocyte production by about 20-30%. This change in blood volume results in a hypervolemic condition in pregnant women where body fluids increase to 6-8 liters with 4-6 liters distributed in the extracellular compartment.
Here are several important roles of pregnancy-induced hypervolemia. They are:
- To fulfill the demands of metabolic needs of an enlarged uterus with a hypertrophic vascularization system
- To provide a lot of nutrients to support the rapid growth of the placenta and fetus
- To protect the mother and fetus from adverse effects due to disruption of venous return in the supine and upright position
- To protect the mother from the adverse effects of blood loss during childbirth.
- Hb and hematocrit concentrations
The condition of hypervolemia is caused by an increase in blood plasma volume and erythrocytes in the circulation. However, due to an increase in erythrocytes, hemodilution occurs and decreasing in hemoglobin (HB) concentration and hematocrit. HB levels initially around 15 gr/dl fall to 12.5 gr/dl, even in 6% of pregnant women can go down to below 11 gr/dl. However, if the concentration of HB below 11 g / dl continues it can indicate an abnormal condition and is usually more often associated with the iron deficiency than hypervolemia.
- Immunological functions
The immune response plays an important role in various reproductive processes such as menstruation, fertilization, pregnancy, and childbirth. Obviously, during pregnancy, when the mother’s body must accept a semi-allogeneic fetus, the immune system plays an important role. Semi-allogeneic fetuses can survive on the body of pregnant women due to immunological interactions between pregnant women and suppressed fetuses. One mechanism that occurs is suppression of T helper (Th) 1 and T cytotoxic (Tc) 1 cell which reduce the secretion of interleukin 2 (IL-2), interferon-γ and tumor necrosis factor (TNF-β).
There is also evidence to suggest that the emphasis on Th-1 is a requirement that pregnancy can continue. However, according to Michimata et al (2003) in Cunningham et al. (2010), not all immune components in the pregnant woman’s body are suppressed or decreased. One example is an increase in Th-2 cells to increase the secretion of IL-4, IL-6, and IL-13. In the cervical mucus, the peak levels of immunoglobulin A and G (IgA and IgG) are higher during pregnancy. Likewise with IL-1β levels in cervical mucus which is ten times greater in pregnant women.
- Coagulation and Fibrinolysis
Pregnancy conditions also affect coagulation and fibrinolysis. In pregnant women, there is a change in the balance of intravascular coagulation and fibrinolysis thus inducing a hypercoagulable state. Procoagulation factors increase at the end of the first trimester, except for factors XI and XII. For example, factors VII, VIII and IX all increase and plasma fibrinogen levels are doubled while antithrombin III, a coagulation inhibitor decreases in number. Protein C, which inactivates factors V and VIII, may not change during pregnancy but the concentration of protein S, one of its cofactors, decreases during the first and second trimesters.
Approximately 5-10% of the total circulating fibrinogen is consumed during placental release. This is what causes thromboembolism. Fibrinolytic plasma activity decreases during pregnancy and childbirth but returns to normal within one hour after placental birth. This shows that control of fibrinolysis during pregnancy is influenced by mediators from the placenta. Normal pregnancy also results in changes in platelet levels. Platelet levels found to be slightly lower during pregnancy were around 213,000 / L compared to 250,000 / L in non-pregnant women. This decrease in platelet levels is partly due to the effects of hemodilution.