Plasma volume increases 45% at term, RBC volume increases 20%, thus while pregnant patients have increased RBC mass, they appear anemic. Normal hemoglobin is 12 g/dl. During labor, contractions squeeze blood into the systemic circulation, and after delivery, uterine involution autotransfuses 500 cc/blood. Note that clotting factors (I, VII, VIII, IX, X, XII) are elevated, protein S (anticoagulant) is decreased, and there is acquired resistance to protein C. Pregnancy is thus a hypercoagulable state. ALSO NOTE THAT both platelet generation and destruction increase, with variable effects. Importantly, 7.6% of term parturients have platelets < 150,000, AND 1% have < 100,000 platelets at term.
References
- R F Burrows, J G Kelton Thrombocytopenia at delivery: a prospective survey of 6715 deliveries. Am. J. Obstet. Gynecol.: 1990, 162(3);731-4 PubMed Link
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