Physiology of Pregnancy Flashcards
Define hypertension in pregnancy
BP >140/90 mmHg
How does circulating blood volume change in pregnancy?
How may this affect the sounds if blood pressure is taken manually?
In pregnancy there is an increase in circulating blood volume
If BP is measured manually in pregnancy there is softening or stopping of korotkoff sounds.
How should blood pressure be measured in a pregnant woman?
Seated, upper arm
What are the 3 types of HTN in pregnancy?
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Essential HTN:
- Occurs before 20 weeks (HTN before pregnancy, detected before 20 weeks)
- Need to change doses of anti-hypertensive medication throughout pregnancy
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Pregnancy induced HTN:
- Increase in BP, no proteinuria
- Returns to normal after pregnancy
-
Pre-eclampsia:
- Raised BP with proteinuria and oedema
Describe the pathophysiology of pre-eclampsia and how this differs to normal pregnancy
In normal pregnancy the trophoblasts invade the myometrium and deciduum. When they invade they replace the endothelium of the spiral arteries which carry the mother’s blood to the pregnancy. They remove the smooth muscle around the arteries, replacing the endothelium with trophoblasts. This causes a decrease in vascular constriction and dilated blood vessels (therefore decreased vascular resistance) which allows the maternal blood to flow slowly in the intervillar space, allowing gas exchange to occur.
If this process does not occur to the normal extent and less of the endothelium is replaced by trophoblasts, the arteries remain narrow as vasoconstriction and high vascular resistance continues. This higher pressure therefore causes the blood flow to remain in higher velocity and there is less opportunity for gas exchange to occur leading to local hypoxia. These processes cause pre-eclampsia which if left untreated leads to the death of both the mother and baby.
Pre-eclampsia = failure of adaptation of the mother to the baby.
Describe normal blood pressure in pregnancy
- Mean arterial pressure reduces at 20 weeks of pregnancy then increases due to increase in placental circulation = increase in circulating blood volume.
- Initial decrease due to new rich vasculature for blood to spread out into
- Therefore susceptible to syncope and dizziness in mid trimester of pregnancy
- Cardiac output increases early in pregnancy (around 10 weeks) due to maternal response to pregnancy rather than the foetal requirement (increases ahead of need)
- Plasma volume also increases 40% up to 20 weeks in pregnancy
- CO increases by increasing stroke volume and heart rate
- Reduction in systemic vascular resistance
Describe renal changes in pregnancy
- Increased blood flow to kidney
- ERPF: effective renal perfusion rate
- = Increased GFR: glomerular filtration rate increased
- = Lower urea levels in pregnant women
Describe the presentation and management of pre-eclampsia
- HTN
- Failure or reduced vascular resistance
- Still responsive to vasoconstrictors
- Reduced circulating volume (due to leaky blood vessels- fluid in extracellular space)
- Failure of renal adaptation to pregnancy
- Reduced GFR
- Proteinuria
- Leaking of glomeruli
- Oedema
- Leaking of capillaries with increased volume and water retention
Management: delivery of the baby
What changes occur in the respiratory system during pregnancy?
Breast and ribcage enlargement
Diaphragm pushed cranially
Increased mucosal engorgement
Normal to have increased respiratory rate in the first 20 weeks due to need for increased CO2 removal. Usually goes unnoticed by the patient.
What are the effects of a raised diaphragm on lung capacities?
Reduction in residual volume (and functional residual capacity) and total lung capacity due to elevation of the diaphragm.
Peak flow, vital capacity and inspiratory capacity should stay the same.
How is the immune system altered in pregnancy?
Reduction in TH1 immunity to tolerate foetus
Increase in TH2 immunity:
- Worsening of asthma
- More susceptibility to viruses
- Improvement in conditions such as rheumatoid arthritis
