Physiological Changes In Pregnancy

Question 1

Progesterone and respiration

Answer 1

Progesterone acts as a respiratory stimulant. Increased levels lead to bronchodilatation, direct stimulation of the respiratory centre, increased sensitivity to CO2, and concentrates carbonic anhydrase in RBCs leading to more pCO2 converted to bicarbonate.

Question 2

Late pregnancy and vital capacity

Answer 2

Remains unchanged, as even though increase in intra-abdominal pressure results in a decrease in residual lung volume, reducing the total capacity by 200mls, diaphragmatic excursion and accessory muscle use increase to maintain the vital capacity.

Question 3

Physiological hyperventilation

Answer 3

Ventilation increases by 49%.
Respiratory capacity is increased due to an increase in tidal volume from 500-700mls.
Hyperventilation leads to breathlessness in over 75%.
Normal respiratory alkalosis due to low CO2 levels.

Question 4

Haemodilution

Answer 4

Occurs due to the disproportionate increase in plasma volume compared to RBC mass.

• plasma volume rises from 6 weeks and stabilises by 32-34 weeks
• RBC mass increases from early second trimester to 20-35% above non pregnant levels by term

Question 5

Hypercoagulable state

Answer 5

1. Increase in concentration of certain clotting factors - factors
   VIII, IX, X, and fibrinogen by up to 50%
2. Decrease in fibrinolytic activity with a fall in concentrations of antithrombin and protein S
3. Coagulation tests however remain the same

Question 6

Pregnancy and bile transport

Answer 6

Oestrogen increases serum cholesterol and this is translated into increased bile salt synthesis.
Progesterone also reduces gallbladder emptying which predisposes to gallstone formation.

Question 7

Renal tract dilatation

Answer 7

Renal calyces, ureters and bladder become dilated due to progesterone acting on smooth muscle and due to compression from gravid uterus.
Due to dextro-rotation owing to the sigmoid colon this causes further dilatation of the right renal system.
Pelvi-calyceal diameter of 5mm on left and 15mm on right is normal, and ureters up to 2cm in the third trimester.

Question 8

Microscopic haematuria in pregnancy

Answer 8

Occurs due to vascular tortuosity in the bladder trigone

Question 9

Insulin antagonists

Answer 9

Cortisol
Progesterone
Oestrogen
Human placental lactogen

Question 10

Iodine in pregnancy

Answer 10

Relative iodine deficiency due to a 2-fold increase in renal loss (increased GFR and decreased reabsorption) and active transport of iodine to the fetus.
Intake of plasma iodide into the thyroid is increased by 3-fold and insufficient dietary intake leads to cellular hyperplasia and goitre