Physiology in Complications of Pregnancy Flashcards
What happens to cardiovascular system in pregnancy?
- Plasma volume increases from 2600 ml to approximately 3800 ml by 32 weeks’ gestation.
- Cardiac output rises by 40%, from about 4.5 l/min to 6 l/min, plateau by 24–30 weeks’ gestation.
- 10% increase in heart rate (from approximately 80 beats per minute to 90 beats per minute) and a larger increase in stroke volume.
What happens to the Respiratory System Pregnancy?
- Ventilation increases by 40% in pregnancy.
- Due to progesterone which acts by stimulating respiratory centre and increasing its sensitivity to carbon dioxide
- Some patients are aware of this increase in ventilation and feel breathless.
- This increase in ventilation is achieved by increasing the tidal volume rather than the respiratory rate.
What leads to changes in ventilation in pregnancy?
- Vital capacity does not change during pregnancy, but the tidal volume expands into the expiratory and inspiratory reserve volume.
- Residual volume decreases by about 200ml, as does the total lung capacity (due to compression from the enlarging uterus).
- There is no change in FEV1, or peak flow rate.
How does pregnancy lead to chronic hyperventilation?
- Alveolar ventilation - ↑ by 70% during the second to third month of gestation.
- Oxygen consumption and carbon dioxide production - both ↑ progressively to reach 60% above non pregnant levels at term.
- The bicarbonate level ↓ to maintain a normal pH and there is a concomitant ↓ in sodium
How does the haematological system change during pregnancy?
- There is an increase in red cell mass, from a non-pregnant level of 1400 ml to 1650–1800 ml.
- Plasma volume increases proportionately more than red cell mass, resulting in a fall in the haematocrit and haemoglobin concentration such that a haemoglobin level of 10.5 g/dl may be within normal limits – physiological anaemia.
- The haemoglobin reaches its nadir at about 32 weeks’ gestation when haemodilution is maximal.
What influences the rate of Gaseous exchange?
Rate proportional to surface area and inversely to the thickness of the villous membrane. Assisted by the double Bohr shift:
- Uterine artery = ~ 90mmHg
- Uterine vein = ~ 45mmHg
- Umbilical art = ~ 20mmHg
- Umbilical vein = ~ 30mmHg
What are features of the placenta?
- A discoid organ 20-25 cm in diameter, 3 cm thick weighing 400-750g.
- Internally it consists of a fetal villous tree bathed directly by maternal blood (villous haemo-chorial type) in the second and third trimesters. Able to hide it HLA to prevent rejection
How does the placenta manipulate the mothers biochemistry?
- Human Chorionic Gonadotrophin (hCG)
- Human Placental Lactogen (hPL)
What are features of the Human chorionic gonadotrophin (hCG)?
- Glycoprotein with two non-covalently linked subunits
- Alpha subunit as in FSH, LH and TSH
- Beta subunit very similar to LH
- Synthesised in the syncytium
- Control unknown but synthesis of beta subunit is rate-limiting
- Acts on LH receptors in corpus luteum and fetal testis – maintains progesterone levels
What are features of Human Placental Lactogen (hPL)?
- 96% sequence homolgy with growth hormone but less growth promoting effects
- Synthesised in the syncytium
- Raises maternal FFAs
- Antagonises peripheral effects of insulin so raises blood glucose levels
- Induces differentiation of mammary glandular tissues
What are definitions of Pre-existing Hypertension, Pregnancy-Induced Hypertension and Pre-eclampsia?
- Pre-existing Hypertension: BP ≥ 140/90 on 2 separate occasions before 20 weeks gestation
- Pregnancy-Induced Hypertension: New hypertension which is BP ≥ 140/90 on 2 separate occasions. Occurs after 20 weeks’ gestation
- Pre-eclampsia: Hypertension PLUS proteinuria (>0.3g in 24hrs or ++ on 2 samples in the absence of UTI)
What is the pathophysiology of Multi-system disorder, pre-eclapmsia in pregnancy?
- Increased capillary permeability
- Reduced plasma volume
- Reduced organ perfusion
What are examples of Maternal Complications?
- Disseminated Intravascular Coagulation
- CVA
- Eclamptic Fit
- Renal Failure
- Liver Failure
- Heart Failure – Pulmonary Oedema
- PE / DVT
- HELLP (Haemolysis, elevated liver enzymes, low platelets)
What is HELLP syndrome?
- Haemolysis, Elevated Liver Function, Low Platelets.
- Associated with cell lysis esp. RBCs.
- Lactate dehydrogenase gives useful measure of severity/recovery in very high 000s.
What are examples of Fetal Complications?
- Fetal Growth Restriction
- Placental Abruption
- Prematurity (Preterm delivery, Iatrogenic)
- Intrauterine Death
How is diagnosis of a foetus made for Pre-Eclampsia?
Placental Growth Factor – Pre-eclampsia
- 287 <35 weeks, PlGF <5th centile had high sensitivity (0.96) and negative predictive value (0.98) for PE in 14 days. Specificity (0.55).
- AUROC for low PlGF (0.87) predicting PE within 14 days was greater than all other commonly used tests.
