Michael C. Gordon
Body Water Metabolism
Salt Metabolism 43
Renin-Angiotensin-Aldosterone System 43
Atrial and Brain Natriuretic Peptide 44
Cardiac Output 45
Arterial Blood Pressure and Systemic
Vascular Resistance 46
Venous Pressure 47
Central Hemodynamic Assessment 47
Normal Changes That Mimic Heart
Effect of Labor and the Immediate
Upper Respiratory Tract 49
Mechanical Changes 49
Lung Volume and Pulmonary Function 49
Gas Exchange 50
Anatomic Changes 54
Renal Hemodynamics 54
Renal Tubular Function/Excretion
of Nutrients 55
Blood Urea Nitrogen
Brain Natriuretic Peptide
Colloidal Oncotic Pressure
Forced Expiratory Volume in
Functional Residual Capacity
Glomerular Filtration Rate
Human Chorionic Gonadotropin
Human Placenta Lactogen
Mean Arterial Pressure
Pulmonary Capillary Wedge
Rapid Eye Movement
Systemic Vascular Resistance
Plasma Volume and Red Blood Cell
Iron Metabolism in Pregnancy 52
Coagulation System 54
Nausea and Vomiting of Pregnancy 57
Calcium Metabolism 58
Skeletal and Postural Changes 59
Adrenal Glands 61
Pituitary Gland 62
Pancreas and Fuel Metabolism
Proteins and Fats/Lipids 62
Major adaptations in maternal anatomy, physiology, and
metabolism are required for a successful pregnancy. Hormonal changes, initiated before conception, significantly alter maternal physiology and persist through both pregnancy and the initial postpartum period. Although these adaptations are profound and affect nearly every organ
system, women return to the nongravid state with minimal
residual changes.1 A full understanding of physiologic
changes is necessary to differentiate between normal alternations and those that are abnormal. This chapter describes maternal adaptations in pregnancy and gives specific
examples of how they may affect care. Finally, although
women may tire of repetitive reassurance that “it is simply normal and of no concern,” a complete understanding
of physiologic changes allows each obstetrician to provide
a more thorough explanation for various changes and
Many of the changes to routine laboratory values caused
by pregnancy are described in the following text. For a
comprehensive review of normal reference ranges for
common laboratory tests by trimester, the reader is encouraged to refer to Appendix A1.
BODY WATER METABOLISM
The increase in total body water of 6.5 to 8.5 L by the end of gestation represents one of the most significant adap
tations of pregnancy. The water content of the fetus, placenta, and amniotic fluid at term accounts for about 3.5 L. Additional water is accounted for by expansion of the
Chapter 3 Maternal Physiology 43
maternal blood volume by 1500 to 1600 mL, plasma volume
by 1200 to 1300 mL, and red blood cells by 300 to 400 mL. The remainder is attributed to extravascular fluid, intracellular fluid in the uterus and breasts, and expanded adipose tissue. As a result, pregnancy is a condition of...
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