14. Maternal physiology and pregnancy Flashcards
What are the main hormones that drive adaptations during pregnancy?
- hCG
- Estrogen
- Progesterone
- Relaxin
- hPL
function of hCG?
maintain corpus lute for oestrogen and progesterone production
why does the level of hCG decrease in the 2nd trimester?
placenta takes over oestrogen and progesterone production so no need to maintain corpus luteum
Is the fetus recognised by the mother immune system?
- Recognised by maternal immune system
- Incited allo-response is not cytotoxic
Why isn’t there a cytotoxic response to the fetus?
- Progesterone and cells of the trophoblastic cells of the placenta produce sHLA-G complex
- induces release of IL10
- IL10 induces formation of Th2 cells from naive CD4+ T helper cells driving balance of T helper cells to regulatory Th2 cells rather than cytotoxic Th1 cells
What conditions may be more/less severe during pregnancy?
- Higher attack rate and severity of certain viral pathogens ie. varicella
- May improve certain autoimmune conditions e.g. psoriasis
What are the respiratory changes?
- Tidal volume increases 30-40%
- respiratory rate stay fairly the same
- Increase PaO2, decrease PCO2
- minute ventilation increased by up to 50%
- ERV decreases 20%
- total lung capacity decreases 5%
What is minute ventilation?
Respiratory Rate x Tidal Volume
- tidal volume increases in pregnancy
What are the changes to partial pressures in pregnancy?
Increase pO2 and decreased pCO2
- pH would increase
Why does the tidal volume increase?
- increase in subcostal angle (from 68 to 103)
- chest diameter increases 2cm or more
- down regulation of residual volume
How does progesterone affect respiratory drive?
Progesterone acts on the respiratory centre, causing sensitisation of the chemoreceptors to CO2 changes leading to increased respiratory effort and reduction in pCO2
When and what causes decreases in total lung capacity?
Later in pregnancy, elevation of diaphragm by about 4cm
What is the normal ABG in pregnancy?
Pregnant women expected to have
(partially) compensated respiratory alkalosis
- high pO2, low pCO2, reduced HCO3-
What is a physiological consequence of changes in the respiratory system and what is most likely due to?
Dysponea of pregnancy
- 60-70% of patients
- Most likely due to progesterone induced hyperventilation and decreased PaCO2
What can distinguish physiological dysponea from pathological dysponea in pregnancy?
- Must be progressive not acute
- should not be present with any other symptoms (e.g. cough, pain)
- chest auscultation should be clear
What are some pathological causes or exacerbating factors of physiological dysponea?
Consider underlying disease (e.g. asthma) • Cardiac • Anemia • DVT/PE ** • Asthma • Pneumonia/ARDS • Pulmonary edema
how are the respiratory needs of the mum and foetus met?
increased ventilation
what are the cardiovascular needs of the mum?
- Fill utero-placental-fetal circulation
- Oxygenate growing uterus - very vascular! High demand
- Protect from impaired venous return
- Prepare for potential blood loss during delivery
how are the cardiovascular needs of mum and foetus met?
Volume expansion
Clotting mechanisms
What are the cardiovascular changes?
- increase in CO
- increase in plasma volume - from 4.5 to 6 L/min
- decrease in total peripheral resistance
- decrease blood pressure (in first 2 trimesters)
What causes increase in cardiac output?
- Early in pregnancy is due to increase in stroke volume
- late is due to increase in heart rate (up to 95 bpm)
What is the normal blood pressure in pregnanacy?
<140/90
What causes fall in total peripheral resistance?
Progesterone causes relaxation of vascular smooth muscle
- causes lower blood pressure in the first and second trimester, but this usually returns to normal by the third trimester.
what can occur in pregnancy due to increased plasma volume/?
Due to the increase plasma vilume, flow murmurs can occur in pregnancy, as well as upward displacement of the apex beat.
