Physiology in Pregnancy Flashcards
Describe how oxygen consumption changes in pregnancy
O2 consumption increases by 15-20%
- 60% maternal
- 40% foetal-placental unit
How does the maternal respiratory system adapt to cope with the change in oxygen requirement?
Hyperventilation; tidal volume is increased to increase minute ventilation. This change is mediated by progesterone.
What are the implications of dyspnoea in pregnancy?
Can be normal, but can be a sign of a pulmonary embolism
Describe how cardiac output changes in pregnancy
Cardiac output increases by about 40% in pregnancy
Both stroke volume and heart rate increase to achieve this CO increase
Describe how peripheral vascular resistance changes in pregnancy
PVR decrease due to vasodilation
Describe how blood pressure changes in pregnancy
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
What is the clinical importance of the rise in blood pressure in the third trimester?
It is important to differentiate between a normal blood pressure rise and a pathological rise due to pre-eclampsia
What is meant by supine hypotension?
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
How do the levels of haemoglobin and red blood cells change in pregnancy?
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
How does the plasma volume change in pregnancy?
Greatly increases
How does the white cell count change in pregnancy?
White cell count increases from “4-11” to “9-15”
How does ESR change in pregnancy?
ESR increases; normal value should be <10, in pregnancy it ranges from 30 to 100.
What drug should be given to reduce the risk of thromboembolic disease in pregnant women? Why is this necessary?
Dalteparin
Pregnancy is a hypercoagulable state
Describe how renal blood flow and GFR change in pregnancy
Increase by 60%
Describe how normal levels of plasma creatinine and urea change in pregnancy
Both fall due to increased GFR:
Creatinine falls from 73 to 47 mmol/L
Urea falls from 4.3 to 3.1 mmol/L
What is the expected level of urate in a pregnant women?
Urate should be no less than ten times the number of weeks gestation
i.e. 36 weeks gestation should have no less than 360
Describe how tubular reabsorption rate changes in pregnancy. What is the clinical significance of this?
Tubular reabsorption rate does not change; this is partly why glycosuria is so common in pregnancy
Give four hormones that are produced by the placenta
Oestrogen
Progesterone
human Placental Lactogen (hPL)
human Chorionic Gonadotrophin (hCG)
What is Mendelson syndrome?
chemical pneumonitis or aspiration pneumonitis caused by aspiration during anaesthesia, especially during pregnancy
Describe the change in gut motility during pregnancy
Gut motility slows, therefore transit times increase
- allows more nutrients to be absorbed by the foetus
Why is there increased incidence/severity of reflux oesophagitis in pregnancy?
Relaxation of lower oesophageal sphincter
Increased intra-abdominal pressure
Which liver enzyme increases in pregnancy? Why?
Alkaline phosphate increases (roughly by double) due to placental production
Why is pregnancy a risk for gallstone formation?
Progesterone is a smooth muscle relaxant and reduces gallbladder emptying
How does resting metabolic rate change in pregnancy?
Resting metabolic rate increases by 20%
