Physiological Changes in Pregnancy

Changes in Volume Homeostasis 

Maternal blood volume expands during pregnancy to allow adequate perfusion of vital organs, including the placenta and fetus, and to anticipate blood loss associated with delivery.
While there is some increase in intracellular water, the most marked expansion occurs in extracellular fluid volume, especially cirrculating plasma volume. This expanded ECF volume accounts for between 8-10 L by the end of pregnancy.

Here are certain factors that contribute to fluid retention:

• Sodium retention
• Resetting of osmostat
• Decreased thirst threshold
• Decreased plasma oncotic pressure

Consequences of fluid retention:

• Decreased Haemoglobin concentration
• Decreased Haematocrit
• Decreased Serum albumin concentration
• Increased Stroke volume
• Increased Renal blood flow

Changes in Blood
There are certain changes in Haematology, Haemostasis and coagulation, Biochemistry and Normal parameters of Blood and blood cells.

There is DECREASE in:

• Hb concentration
• Haematocrit
• Plasma folate concentration
• Protein S activity
• Plasma protein concentration
• Creatinine, urea and uric acid

And INCREASE in:

• ESR
• Fibrinogen concentration
• Activated protein C resistance
• Factors VII, VIII, IX, X and XII
• D-dimers
• Alkaline Phosphatase

Changes in The Respiratory Tract:
Ventilatory changes:

• Thoracic anatomy changes
• Increased Minute ventilation
• Increased Tidal volume
• Decreased Residual volume
• Decreased Functional residual capacity
• Vital capacity unchanged or slightly changed

Blood gas and acid-base changes:

• Decreased pCO2
• Increased O2
• pH alters little
• Increased Bicarbonate excretion
• Increased Oxygen availability to tissues and placenta

Cardiovascular changes

• Increased Heart rate (10-20%)
• Increased Stroke volume (10%)
• Increased Cardiac output (30-50%)
• Decreased Mean arterial pressure (10%)
• Decreased Pulse pressure
• Decreased Peripheral resistance (35%)

Endocrine Changes:

• Increased Prolactin concentration
• Human growth hormone is suppressed
• Increased Corticosteroid concentrations
• Decreased TSH in early pregnancy
• Decreased fT4 in late pregnancy
• hCG is produced
• Insulin resistance develops

GIT changes

• Progesterone induces cravings
• Increased absorption of calcium and iron
• lower and upper intestines raised
• decreased motility of GIT (increased absorption, but leads to constipation)
• reduced tone of lower oesophageal sphincter (due to progesterone, leads to heartburn)
• increased volume and contraction of gull bladder (leads to kidney stones)

 

Renal Changes

• Increased blood flow (40%)
• Increased plasma flow (45%)
• Increased glomerular filtration rate (50% - due to increased plasma flow and reduction in colloid osmotic pressure)
• Reduced levels of creatine and urea in plasma
• Failure to reabsorb all filtered glucose - glycosuria
• Amino acid excretion increased
• Increased sodium retention (largely due to activation of renal angiotensin system) 
• Increased water retention

 

Metabolic changes in pregnancy 

Basal metabolic rate (BMR)
BMR increase to 20% above non-pregnant state at 36 weeksFalls slightly to 15% above non-pregnant state baseline at term.
Oxygen consumption
Oxygen consumption increase by 20% at term.
Carbohydrate metabolism
Insulin secretion increase from end of first trimester to 32 weeks, then declines to non-pregnant level at term
Impaired glucose tolerance
Tissue sensitivity to insulin diminishesIncreased level of hPL, free cortisol, oestrogen and progesterone may contribute
Fat metablism
Net storage of fat in the first half of pregnancy--> Decreased FFA and glycerol in plasmaMobilisation during second half --> Increased FFA and glycerol in plasma
Amino acid metabolism
Maternal plasma level of amino acid falls due to Gluconeogenesis.

 

Skin Changes:

•  Hyperpigmentation

• Striae gravidarum

• Hirsuitism

• Increased Sebaceous gland activity.

   

  Here is the Summary of Physiological Changes in Pregnancy in tabulated form: