Hematologic changes of pregnancy

Berhanu MohammedApril 21, 2011

Hematology

Definition• Components of blood

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Components of blood

• Plasma– Transport mechanism

• 90-92% water. • 6-7% proteins• 2-3%

– Fats– Carbohydrates (glucose)– Electrolytes– Gases (O2, CO2)– Chemical messengers

Plasma Components

Other3%

Protein7%

Water90%

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Functions

• responsible for the transport of blood gases from the lung to the tissues (oxygen) and from the tissues back to the lungs (carbon dioxide).

• White blood cells serve to defend against pathogens and foreign bodies(immunity). They perform these tasks most of the time outside theblood vessels, in the connective tissues. In this case the blood serves solely as a means of transportation from the site of cell formation (bonemarrow) to the site of action.

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Cellular Components

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Components of blood

• Red Blood Cells– Erythrocyte

• Hemoglobin – O2 bearing molecule

– Comprised of 4 subunits:

» Globin (binds to 1 O2 molecule)

» Heme (iron)– 100% saturation = 4

globin subunits carrying O2

» Each gram of hemoglobin = 1.34 ml O2

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Fig. Formation of the multiple different blood cells from the original pluripotent hematopoietic stem cell (PHSC) in the bone marrow.04/13/2023

Fig. Genesis of normal red blood cells (RBCs) and characteristics of RBCs in different types of anemias.04/13/2023

Fig. Function of the erythropoietin mechanism to increase production of red blood cells when tissue oxygenation decreases.04/13/2023

Genesis of white blood cells04/13/2023

• Platelets (Thrombocytes)– Megakaryocytes

• Thrombopoietin

– Thrombocytopenia– Thrombocytosis

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Hemostasis

hemostasis is achieved by several mechanisms:1) vascular constriction, 2) formation of a platelet plug, 3) formation of a blood clot as a result of blood

coagulation, and4) eventual growth of fibrous tissue into the

blood clot to close the hole in the vessel permanently.

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Fig. Clotting process in a traumatized blood vessel.

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Schema for conversion of prothrombin to thrombin and polymerizationof fibrinogen to form fibrin fibers

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Extrinsic pathway for initiating blood clotting

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Ca++Intrinsic pathway for initiating blood clotting04/13/2023

Pregnancy changes

The Most significant changes are:• Physiologic anemia• Neutrophilia • Mild thrombocytopenia • Increased procoagulant factors • Diminished fibrinolysis

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Plasma volume

• Increased by 10 to 15 % • Total gain at term averages 1100 to 1600mlTotal volume 4700ml to 5200ml ,i.e. 30 to 50% above non pregnant , Fig.1

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Fig.1

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Plasma Volume

Systemic vasodilatation

Rise in vascular capacitance

Underfilled vascular system

Rise in plasma volume

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Pregnancy-induced hypervolemia has important functions:

• To meet the metabolic demands of the enlarged uterus & hypertrophied vascular system.

• To provide an abundance of nutrients and elements to support the rapidly growing placenta and fetus.

• To protect the mother and in turn the fetus, against the deleterious effects of impaired venous return in the supine and erect positions.

• To safeguard the mother against the adverse effects of blood loss associated with parturition.

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Plasma Volume during postpartumDecreases

after delivery ,then increases

again 2 to 5 days later

10 to 15%

above

at 3 weeks

Nl at 6 wks

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RED BLOOD CELLS

• 20 to 30% (250 to 450 mL) above nonpregnant iron supplemented

• 15 to 20% above nonpregnant not on iron supplement

• Life span slightly decreased • Erythropoietin levels increase by 50 %

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Fig. Erythropoietin levels in response to anemia

physiological or dilutional anemia of pregnancy

• Observed in healthy pregnant woman• Greatest during late 2nd to early 3rd trimester

lowest Hgb at 28 to 36wks • Nearer to term Hgb increases• Anemia cut off point: <11 g/dL 1st and 3rd

trimesters and < 10.5 g/dL 2nd trimester, for black Americans 0.8g/dl less

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Hemoglobin Values in Pregnancy

WEEKS' GESTATION

MEAN HEMOGLOBIN (G/DL)

FIFTH PERCENTILE HEMOGLOBIN (G/DL)

12 12.2 11.0

16 11.8 10.6

20 11.6 10.5

24 11.6 10.5

28 11.8 10.7

32 12.1 11.0

36 12.5 11.4

40 12.9 11.9

From U.S. Department of Health and Human Services: Recommendations to prevent and control iron deficiency in the United States. MMWR 47:1, 1998

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PLATELET COUNT

• Mean PLT slightly lower than healthy non pregnant woman

due to the effects of hemodilutionincreased platelet consumption

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Thrombocytopenia

• most significant obstetrical consideration concerning platelet physiology in pregnancy

• Gestational or incidental thrombocytopenia is characterized : mild asymptomatic occurring in the third trimester without any historynot associated with maternal, fetal, or neonatal

sequelae and spontaneously resolves postpartum Platelet counts are typically >70,000/microL, with

about two-thirds being 130,000 to 150,000 microL

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WHITE BLOOD CELLS

• 1st trimester, the mean count is 8,000/mm3, Nl (5,110 to 9,900/mm)

• 2nd & 3rd trimester, the mean is 8,500/mm3, Nl (5,600 to 12,200/mm3

• In labor, rise to 20,000 to 30,000/mm3, • largely due to increases in circulating segmented

neutrophils and granulocytes• caused by the elevated estrogen and cortisol levels • Returns to normal with in 1 to 2 weeks

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Immunologic system • associated with suppression humoral and cell-

mediated immunological functions • involve suppression of T-helper (Th) 1 and T-

cytotoxic (Tc) 1 cells, which decreases secretion of interleukin-2 (IL-2), interferon- , and tumor necrosis factor- (TNF-)

• upregulation of Th2 cells to increase secretion of IL-4, IL-6, and IL-13.

• In cervical mucus,immunoglobulins A and G (IgA and IgG) are significantly higher

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COAGULATION FACTORS AND INHIBITORS

• 5 to 6 fold increased risk for thromboembolic disease• venous stasis, vessel wall injury, and changes in the

coagulation cascade• Fibrinogen, factors II, VII, VIII, X, XII, and XIII increase

by 20 to 200 percent • Von Willebrand factor increases• Antithrombin, protein C, Factor V and Factor IX levels

remain unchanged or increase slightly• return to baseline by six to eight weeks after delivery

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Table 5-2. Changes in Measures of Hemostasis during Normal Pregnancy

Parameter Nonpregnant Pregnant (35–40 weeks)

Activated PTT (sec) 31.6 ± 4.9 31.9 ± 2.9

Thrombin time (sec) 18.9 ± 2.0 22.4 ± 4.1a

Fibrinogen (mg/dL) 256 ± 58 473 ± 72a

Factor VII (%) 99.3 ± 19.4 181.4 ± 48.0a

Factor X (%) 97.7 ± 15.4 144.5 ± 20.1a

Plasminogen (%) 105.5 ± 14.1 136.2 ± 19.5a

tPA (ng/mL) 5.7 ± 3.6 5.0 ± 1.5

Antithrombin III (%) 98.9 ± 13.2 97.5 ± 33.3

Protein C (%) 77.2 ± 12.0 62.9 ± 20.5a

Total Protein S (%) 75.6 ± 14.0 49.9 ± 10.2a

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Figure 3-11  The normal components of the coagulation cascade.  (From Johnson RL: Thromboembolic disease complicating pregnancy. In Foley MR, Strong TH [eds]: Obstetric Intensive Care: A Practical Manual. Philadelphia, WB Saunders Company, 1997, p 91, with permission.)

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Key points Maternal plasma volume increases 50 percent

during pregnancy RBC volume increases approximately 18 to 30

percenthematocrit normally decreases during gestation but

not below 30 percent Pregnancy is a hypercoagulable state increases in the levels of the majority of the procoagulant factors increase and fibrinolytic system decreases and in some of the

natural inhibitors of coagulation04/13/2023

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References

• Guyton and Hall ,Text book of medical physiology , 11th edition

• Williams Obstetrics,Cunningham, Leveno, Bloom, Hauth, Rouse, Spong, 23rd edition

• Obstetrics normal and problem pregnancies, Steven G. Gabbe,Jennifer R.Niebyl, Joe leigh simpson, 5th Edition

• Up to date , 18.2

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Thank you

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