Physiology in Pregnancy

Question 1

Describe how oxygen consumption changes in pregnancy

Answer 1

O2 consumption increases by 15-20%

• 60% maternal
• 40% foetal-placental unit

Question 2

How does the maternal respiratory system adapt to cope with the change in oxygen requirement?

Answer 2

Hyperventilation; tidal volume is increased to increase minute ventilation. This change is mediated by progesterone.

Question 3

What are the implications of dyspnoea in pregnancy?

Answer 3

Can be normal, but can be a sign of a pulmonary embolism

Question 4

Describe how cardiac output changes in pregnancy

Answer 4

Cardiac output increases by about 40% in pregnancy

Both stroke volume and heart rate increase to achieve this CO increase

Question 5

Describe how peripheral vascular resistance changes in pregnancy

Answer 5

PVR decrease due to vasodilation

Question 6

Describe how blood pressure changes in pregnancy

Answer 6

Early pregnancy: BP initially falls slightly because the decreased PVR is not quite compensated for by the increased CO
Late pregnancy: BP may rise slightly in third trimester

Question 7

What is the clinical importance of the rise in blood pressure in the third trimester?

Answer 7

It is important to differentiate between a normal blood pressure rise and a pathological rise due to pre-eclampsia

Question 8

What is meant by supine hypotension?

Answer 8

Blood pressure drops when lying supine. Occurs in late pregnancy and is due to restricted venous return caused by the uterus pressing on and occluding the inferior vena cava

Question 9

How do the levels of haemoglobin and red blood cells change in pregnancy?

Answer 9

Mass of Hb and RBCs increase in pregnancy, but there is a greater increase in plasma volume therefore concentrations of Hb and RBCs is seen to decrease:

Hb decreases from 130-110 g/L
RCC decreases from 4.2 to 3.7 x10^12/L

Question 10

How does the plasma volume change in pregnancy?

Answer 10

Greatly increases

Question 11

How does the white cell count change in pregnancy?

Answer 11

White cell count increases from “4-11” to “9-15”

Question 12

How does ESR change in pregnancy?

Answer 12

ESR increases; normal value should be <10, in pregnancy it ranges from 30 to 100.

Question 13

What drug should be given to reduce the risk of thromboembolic disease in pregnant women? Why is this necessary?

Answer 13

Dalteparin

Pregnancy is a hypercoagulable state

Question 14

Describe how renal blood flow and GFR change in pregnancy

Answer 14

Increase by 60%

Question 15

Describe how normal levels of plasma creatinine and urea change in pregnancy

Answer 15

Both fall due to increased GFR:
Creatinine falls from 73 to 47 mmol/L
Urea falls from 4.3 to 3.1 mmol/L

Question 16

What is the expected level of urate in a pregnant women?

Answer 16

Urate should be no less than ten times the number of weeks gestation
i.e. 36 weeks gestation should have no less than 360

Question 17

Describe how tubular reabsorption rate changes in pregnancy. What is the clinical significance of this?

Answer 17

Tubular reabsorption rate does not change; this is partly why glycosuria is so common in pregnancy

Question 18

Give four hormones that are produced by the placenta

Answer 18

Oestrogen
Progesterone
human Placental Lactogen (hPL)
human Chorionic Gonadotrophin (hCG)

Question 19

What is Mendelson syndrome?

Answer 19

chemical pneumonitis or aspiration pneumonitis caused by aspiration during anaesthesia, especially during pregnancy

Question 20

Describe the change in gut motility during pregnancy

Answer 20

Gut motility slows, therefore transit times increase

- allows more nutrients to be absorbed by the foetus

Question 21

Why is there increased incidence/severity of reflux oesophagitis in pregnancy?

Answer 21

Relaxation of lower oesophageal sphincter

Increased intra-abdominal pressure

Question 22

Which liver enzyme increases in pregnancy? Why?

Answer 22

Alkaline phosphate increases (roughly by double) due to placental production

Question 23

Why is pregnancy a risk for gallstone formation?

Answer 23

Progesterone is a smooth muscle relaxant and reduces gallbladder emptying

Question 24

How does resting metabolic rate change in pregnancy?

Answer 24

Resting metabolic rate increases by 20%

Question 25

Describe how and why insulin sensitivity changes in early pregnancy

Answer 25

Sensitivity increases:

• increased glycogen synthesis
• increased fat deposition
• increased transfer of amino acids into cells

Question 26

Describe how and why insulin sensitivity changes in late pregnancy

Answer 26

Sensitivity decreases; mother becomes slightly insulin resistant

• serum glucose level increases (which allows foetal glucose level to increase)
• serum lipid levels increase
• maternal amino acid levels fall but there in increased amino acid transfer across the placenta

Question 27

Give four pregnancy-related hormones which are insulin antagonists

Answer 27

Cortisol
Progesterone
Oestrogen
hPL