Coupon Accepted Successfully!


Physiological Changes in Pregnancy

Early changes are due to the metabolic demands brought on by the fetus, placenta and uterus and, in part, to the increasing levels of pregnancy hormones, particularly those of progesterone and oestrogen.

Later changes, starting in mid - pregnancy, are anatomical i nature and are caused by mechanical pressure from the expanding uterus.

  1. Hematological changes
    Blood volume (mL) Increased +30-40%
    Plasma volume (mL) Increased +40-50%
    RBC volume (mL) Increased +20-30%
    Total Hb (g) Increased +20%
    Hb (g%) PCV (%) Decreased -20%
  2. Plasma protein changes in pregnancy
    1. Total protein (g) Increased +20-30%
    2. Plasma protein concentration (g%) Decreased -10%
    3. Albumin (g%) Decreased -30%
    4. Globulin (g%) Slight increase +5%
    5. Albumin: globulin ratio Decreased -
  3. Blood coagulation factors
    Increased Decreased Unaffected
    Fibrinogen (+50%) Factor XI Clotting time
    ESR (4 times) Factor XIII Bleeding time
    Factor IX Platelet count

Platelet count slightly decreases during pregnancy; however, there is no decline in platelet function.

  1. Respiratory system changes if pregnancy
    Increased Decreased Unaffected
    Tidal volume Functional residual capacity Respiratory rate
    Minute ventilation Expiratory reserve volume Vital capacity
    Minute O2 uptake Residual volume Inspiratory reserve volume
    Inspiratory capacity Total lung capacity
  2. Renal changes in pregnancy



Renal blood flow (+50%)

S. creatinine

GFR (+50%)


Creatinine clearance

S. uric acid


Plasma osmolality

Aminoacid uria

S. Na+ / K+ / Cl-

  • S. aldosterone increases in pregnancy.
  • S. ADH (antidiuretic hormone) remains unchanged in pregnancy.
  1. Cardiac output increases by 40% during pregnancy, 50% during each uterine contraction in labor, and 80% immediately postpartum (as the uterus contracts, blood from uterus is pushed back into the maternal system, also known as "autotransfusion"), Therefore the risk of cardiac failure is maximum in the immediate postpartum period (followed by intrapartum). To avoid this, diuretics should be given after placental delivery to heart disease patients.
    1. The cardiac output begins to rise from 8 weeks of gestation and reaches its peak at 28-30 weeks.
    2. So the maximum risk of a heart disease patient to have cardiac failure during pregnancy is at 32 weeks.
  2. Iron requirements: The iron requirements of normal pregnancy total approximately 100 mg. About 300 mg are actively transferred to the fetus and placenta, and about 200 mg are lost through vanous normal routes of excretion, primarily the gastrointestinal tract. The average increase in the total volume of circulating erythrocytes-about 450 mL during pregnancy when iron is available-uses another 500 mg of iron, because 1 mL of normal erythrocytes contains 1.1 mg of iron. The iron requirement during the second half of pregnancy is 6-7 mg/day.

Changes in Iron Metabolism during Pregnancy:



  1. Serum Iron concentration
  2. Serum ferritin (Reflecting Iron stores)
  3. Serum Total iron binding capacity
  4. Percentage saturation (Serum ferritin /TIBC)
  5. Serum Transferrin
  1. Decreases
  2. Decreases
  3. Increases
  4. Decreases
  5. Increases
  1. Normal pregnancy is characterized by mild fasting hypoglycemia, postprandial hyperglycemia, and hyperins-ulinemia.
  2. During pregnancy, the pH becomes 7.42 (during nonpregnant state pH is 7.4). Pregnancy is a state of respiratory alkalosis with metabolic acidosis.

NOTE: From about the 7th to the 18th day of the menstrual cycle, a fern-like pattern of dried cervical mucus is seen.

After approximately the 21st day, a different pattern forms that gives a beaded or cellular appearance. This beaded pattern is also usually encountered during pregnancy. The crystallization of the mucus, which is necessary for the production of the fern pattern, is dependent on an increased concentration of sodium chloride.


Cervical mucus is relatively rich in sodium chloride when estrogen, but not progesterone, is being produced.

Progesterone secretion even without a reduction in estrogen secretion acts promptly to lower sodium chloride concentration to levels at which ferning will not occur.


During pregnancy, progesterone usually exerts a similar effect, even though the amount of estrogen produced is enormous. Thus, if copious thin mucus is present and if a fern pattern develops on drying early pregnancy is unlikely.


Extra Edge:

Increase during pregnancy

Decrease during pregnancy

a. Hemoglobin mass

Hemoglobin concentration

b. Total plasma protein

Factor XI and XIII

c. Globulin

All parameters of iron metabolism except TIBC & transferrin

d. Leucocytes (Neutrophilic leucocytosis)


e. Fibrinogen

f. Factors II, VII, VIII, IX, X

g. Insulin

h. Lipids, lipoproteins (LDL and HDL)

& apolipo-proteins

Serum Blood Urea Nitrogen

i. Serum Transferrin and TIBC.

Serum Na / K / Ca / Mg /I2

j. C Reactive protein


k. Placenta Phosphatase


l. Total Alkaline Phosphatase


Test Your Skills Now!
Take a Quiz now
Reviewer Name