Physiology of Pregnancy Flashcards
At what point do massive cardiovascular changes occur in development? and when do they plateau?
Start at 6 weeks, plateau at 2nd trimester
What are the weeks associated with the first, second and third trimesters of pregnancy?
First trimester: week 1-12
Second trimester: week 13-28
Third trimester: weel 29-40
First 12 weeks, 16 weeks, Last 12 weeks
To what degree do cardiovascular changes occur during pregnancy? Use Starling’s law.
Starling’s law: CO = SV x HR
CO = 30-50% increase (4.5L/min → 6L/min)
SV = 30%
HR = 15% (〜10bpm)
Blood volume is 150% of non-pregnant
How does CO change in regards to the following:
Preload
Afterload
Distribution
Demands of labour
Immediate post-partum
↑blood volume → ↑Preload
↓SVR → ↓Afterload
Uterus: 〜400mL/min; Kidneys: 〜300mL/min
Demands of labour: ↑15-50% increase
Immediate post-partum: ↑80% - increased amount in circulation as placenta removed (uterus contracts)
Why should a pregnant woman not be left lying down in supine position?
IVC compression
How does peripheral vascular resistance fall during pregnancy?
Progesterone effect → smooth muscle relaxation
How much is BP affected in the first 24 weeks of pregnancy?
Systolic BP ↓5-10
Diastolic BP ↓10-15
How long does it take for CO and SVR to return to normal after pregnancy?
3 months
How does the renin angiotensin aldosterone system become involved with CVS changes?
Increase RAAS activity → Retention of H2O and Na+
Peripheral oedema
Raised intravascular volume
When examining a pregnant woman, what are normal clinical features which would be abnormal in a non-pregnant woman?
Palpitations
Dyspnoea
Oedema
CXR changes (Cardiac rotation/oedema)
What heart changes can be found on auscultation of a pregnant mother’s heart?
3rd Heart sound
Soft systolic flow murmur
What are normal ECG changes seen in pregnant women?
Borderline Sinus Tachycardia
Left axis deviation
ST changes and inversion of T wave in leads III, aVF
To what extent does blood volume change in pregnancy? when does it start? and when does it reach its maximal volume?
2600ml to 5000ml
Starts early (progesterone/RAAS) and is maximal at around 32 weeks
How do blood constituents change in pregnancy?
Neutrophils
Platelets
Immune function
RBCs
Ferritin
Neutrophilia (↑Neutrophils)
Reduced platelet count
Cell-mediated immune function depresses, count not affected
RBC mass ↑ 30% - but relative to volume increase - Haematocrit and Hb decrease
Ferritin decreases
`How do plasma proteins change in pregnancy?
Total protein
Albumin
Gamma globulin
ALP
Beta globulin
Fibrinogen
ESR
Total protein, Albumin, Gamma globulin ↓ - Reduction in intravascular proteins exacerbate peripheral oedema
ALP ↑
beta globulin and fibrinogen ↑ (ESR x4)
How do the haematological changes in pregnancy help?
Hypervolaemia → Improved laminar flow → Good placental perfusion → Reduced cardiac work
increased reserve to allow for intrapartum blood loss
How can we be particularly careful with anaemia in pregnancy?
Symptoms of dyspnoea, oedema, tiredness
Early consideration of iron supplementation
How does the coagulation system adapt in pregnancy?
Prothrombotic state:
↑Factors I (fibrinogen), VII, VIII, IX, X, XII - Protect from haemorrhage at delivery, but risk of thromboembolism
Increased resistance to activated protein C
Reduced protein S
Reduced PT and partial thromboplastin times
What happens in the coagulation system during the 3rd trimester?
Increase in Factor VIII platelet aggregation and coagulation
How well do women tolerate haemorrhage in pregnancy?
It is well tolerated in general
Tolerate 1.5L then rapid decompensation - loss need accurate monitoring - early volume replacement/oxygen carrying capacity/clotting factors
What factors of spirometry and breathing are altered and kept the same in pregnancy?
↑ Tidal Volume
↓ Residual Volume
RR and Vital capacity unchanged
How does compensated respiratory alkalosis help in pregnancy?
Facilitates foeto-maternal O2 transfer at placental interface
How does progesterone affect the pregnant mother in terms of the respiratory function?
Subjective feeling of SOB
Exacberated by rising fundus with advancing gestation
What happens to the kidney during pregnancy?
It increases in size - hypertrophy and hyperplasia of functional compartments
Also hydronephrosis
What happens to the ureters in pregnancy?
They dilate as there is a mechanical obstruction at the pelvic brim
It also affects smooth muscle → decreased peristalsis and contraction pressure
How does the renal physiology change in pregnancy?
Renal blood flow, GFR, Tubular function, U+Es
Plasma renin, ATII, aldosterone
Renal blood flow ↑ 75-80%
GFR ↑ 150% of non-pregnant rate by mid-trimester
Tubular function: ↑glycosuria, proteinuria, calciuria, bicarbonaturia
Urea and Creatinine ↓ with ↑ Creatinine clearance
↑Renin, ATII, Aldosterone - but reduced vascular sensitivity, so maintains pulmonary vascular resistance
How is the bladder capacity affected in pregnancy?
It is decreased - urinary frequency ↑ and nocturia
It becomes an intra-abdominal organ - important to empty in labour
How is the lower oesophageal sphincter affected in pregnancy?
Progesterone affects the LOS → reflux
How is GI motility affected in pregnancy?
It is reduced, due to oestrogen and progesterone - slower transit, better absorption, constipation
What is Mendelson’s Syndrome?
Peptic Aspiration Pneumonia
How is thyroid function affected in pregnancy?
↑Thyroxine-Binding Globulin → ↓free T4 → ↑TSH → ↑T3/4 production
A high hCG will bind to the TSH receptor → suppression
May get transient hyperthyroidism
