Maternal Physiology

Topics: Blood pressure, Respiratory physiology, Sleep Pages: 24 (21002 words) Published: April 15, 2015
CHAPTER 3

Maternal Physiology
Michael C. Gordon

Body Water Metabolism 

42

Osmoregulation  43
Salt Metabolism  43
Renin-Angiotensin-Aldosterone System  43
Atrial and Brain Natriuretic Peptide  44

Cardiovascular System 

44

Heart  44
Cardiac Output  45
Arterial Blood Pressure and Systemic
Vascular Resistance  46
Venous Pressure  47
Central Hemodynamic Assessment  47
Normal Changes That Mimic Heart
Disease  47
Effect of Labor and the Immediate
Puerperium  48

Respiratory System 

49

Upper Respiratory Tract  49

Mechanical Changes  49
Lung Volume and Pulmonary Function  49
Gas Exchange  50
Sleep  51

Hematologic Changes 

Urinary System 

42

54

Anatomic Changes  54
Renal Hemodynamics  54
Renal Tubular Function/Excretion  
of Nutrients  55

Alimentary Tract 
Appetite  56

KEY ABBREVIATIONS
Adrenocorticotropic Hormone
Arginine Vasopressin
Blood Urea Nitrogen
Brain Natriuretic Peptide
Carbon Dioxide
Cardiac Output
Colloidal Oncotic Pressure
Corticotropin-Releasing Hormone
Forced Expiratory Volume in
1 Second
Functional Residual Capacity
Glomerular Filtration Rate
Human Chorionic Gonadotropin
Human Placenta Lactogen
Mean Arterial Pressure
Parathyroid Hormone
Pulmonary Capillary Wedge
Pressures
Rapid Eye Movement
Renin-Angiotensin-Aldosterone
System
Stroke Volume
Systemic Vascular Resistance
Thyroid-Stimulating Hormone
Thyroxine-Binding Globulin
Total Thyroxine
Total Triiodothyronine

51

Plasma Volume and Red Blood Cell
Mass  51
Iron Metabolism in Pregnancy  52
Platelets  53
Leukocytes  53
Coagulation System  54

ACTH
AVP
BUN
BNP
CO2
CO
COP
CRH
FEV1
FRC
GFR
hCG
hPL
MAP
PTH
PCWPs
REM
RAAS
SV
SVR
TSH
TBG
TT4
TT3

56

Mouth  56
Stomach  56
Intestines  57
Gallbladder  57
Liver  57
Nausea and Vomiting of Pregnancy  57

Skeleton 

58

Calcium Metabolism  58
Skeletal and Postural Changes  59

Endocrine Changes 
Thyroid  59
Adrenal Glands  61
Pituitary Gland  62

59

Pancreas and Fuel Metabolism 
Glucose  62
Proteins and Fats/Lipids  62

Eye 

62

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
symptoms.
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
142
140
PNa (mmol/L)

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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