Physiology of Pregnancy

Question 1

At what point do massive cardiovascular changes occur in development? and when do they plateau?

Answer 1

Start at 6 weeks, plateau at 2nd trimester

Question 2

What are the weeks associated with the first, second and third trimesters of pregnancy?

Answer 2

First trimester: week 1-12

Second trimester: week 13-28

Third trimester: weel 29-40

First 12 weeks, 16 weeks, Last 12 weeks

Question 3

To what degree do cardiovascular changes occur during pregnancy? Use Starling’s law.

Answer 3

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

Question 4

How does CO change in regards to the following:

Preload

Afterload

Distribution

Demands of labour

Immediate post-partum

Answer 4

↑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)

Question 5

Why should a pregnant woman not be left lying down in supine position?

Answer 5

IVC compression

Question 6

How does peripheral vascular resistance fall during pregnancy?

Answer 6

Progesterone effect → smooth muscle relaxation

Question 7

How much is BP affected in the first 24 weeks of pregnancy?

Answer 7

Systolic BP ↓5-10

Diastolic BP ↓10-15

Question 8

How long does it take for CO and SVR to return to normal after pregnancy?

Answer 8

3 months

Question 9

How does the renin angiotensin aldosterone system become involved with CVS changes?

Answer 9

Increase RAAS activity → Retention of H₂O and Na⁺

Peripheral oedema

Raised intravascular volume

Question 10

When examining a pregnant woman, what are normal clinical features which would be abnormal in a non-pregnant woman?

Answer 10

Palpitations

Dyspnoea

Oedema

CXR changes (Cardiac rotation/oedema)

Question 11

What heart changes can be found on auscultation of a pregnant mother’s heart?

Answer 11

3rd Heart sound

Soft systolic flow murmur

Question 12

What are normal ECG changes seen in pregnant women?

Answer 12

Borderline Sinus Tachycardia

Left axis deviation

ST changes and inversion of T wave in leads III, aVF

Question 13

To what extent does blood volume change in pregnancy? when does it start? and when does it reach its maximal volume?

Answer 13

2600ml to 5000ml

Starts early (progesterone/RAAS) and is maximal at around 32 weeks

Question 14

How do blood constituents change in pregnancy?

Neutrophils

Platelets

Immune function

RBCs

Ferritin

Answer 14

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

Question 15

`How do plasma proteins change in pregnancy?

Total protein

Albumin

Gamma globulin

ALP

Beta globulin

Fibrinogen

ESR

Answer 15

Total protein, Albumin, Gamma globulin ↓ - Reduction in intravascular proteins exacerbate peripheral oedema

ALP ↑

beta globulin and fibrinogen ↑ (ESR x4)

Question 16

How do the haematological changes in pregnancy help?

Answer 16

Hypervolaemia → Improved laminar flow → Good placental perfusion → Reduced cardiac work

increased reserve to allow for intrapartum blood loss

Question 17

How can we be particularly careful with anaemia in pregnancy?

Answer 17

Symptoms of dyspnoea, oedema, tiredness

Early consideration of iron supplementation

Question 18

How does the coagulation system adapt in pregnancy?

Answer 18

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

Question 19

What happens in the coagulation system during the 3rd trimester?

Answer 19

Increase in Factor VIII platelet aggregation and coagulation

Question 20

How well do women tolerate haemorrhage in pregnancy?

Answer 20

It is well tolerated in general

Tolerate 1.5L then rapid decompensation - loss need accurate monitoring - early volume replacement/oxygen carrying capacity/clotting factors

Question 21

What factors of spirometry and breathing are altered and kept the same in pregnancy?

Answer 21

↑ Tidal Volume

↓ Residual Volume

RR and Vital capacity unchanged

Question 22

How does compensated respiratory alkalosis help in pregnancy?

Answer 22

Facilitates foeto-maternal O2 transfer at placental interface

Question 23

How does progesterone affect the pregnant mother in terms of the respiratory function?

Answer 23

Subjective feeling of SOB

Exacberated by rising fundus with advancing gestation

Question 24

What happens to the kidney during pregnancy?

Answer 24

It increases in size - hypertrophy and hyperplasia of functional compartments

Also hydronephrosis

Question 25

What happens to the ureters in pregnancy?

Answer 25

They dilate as there is a mechanical obstruction at the pelvic brim

It also affects smooth muscle → decreased peristalsis and contraction pressure

Question 26

How does the renal physiology change in pregnancy?

Renal blood flow, GFR, Tubular function, U+Es

Plasma renin, ATII, aldosterone

Answer 26

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

Question 27

How is the bladder capacity affected in pregnancy?

Answer 27

It is decreased - urinary frequency ↑ and nocturia

It becomes an intra-abdominal organ - important to empty in labour

Question 28

How is the lower oesophageal sphincter affected in pregnancy?

Answer 28

Progesterone affects the LOS → reflux

Question 29

How is GI motility affected in pregnancy?

Answer 29

It is reduced, due to oestrogen and progesterone - slower transit, better absorption, constipation

Question 30

What is Mendelson’s Syndrome?

Answer 30

Peptic Aspiration Pneumonia

Question 31

How is thyroid function affected in pregnancy?

Answer 31

↑Thyroxine-Binding Globulin → ↓free T4 → ↑TSH → ↑T3/4 production

A high hCG will bind to the TSH receptor → suppression

May get transient hyperthyroidism