PHYSIOLOGY IN PREGNANCY

1. Physiological changes in pregnancy

2. Maternal adaptations to pregnancy
Profound anatomical, physiological and
biochemical changes occur during pregnancy
Purpose is to support growth of the fetus and
prepare the mother for delivery and lactation
Some of the adaptations may be considered
abnormal if the patient was not pregnant
Normal adaptations can be misinterpreted as
disease
Pregnancy adaptations can unmask or worsen
pre-existing disease

3. Uterine changes
Progressive uterine enlargement
 Helps in gestational dating
 Helps in assessing fetal growth
 Occurs in ectopic pregnancy also
 Contributes to pedal edema by occluding venous
return
Supine hypotension
 Due to vena caval compression
 Occurs in women with poor collateral circulation

4. Haemodynamic changes
Increased intra-vascular volume
 Blood volume
○ Increased by 40 - 45% ( appx 1.5 litres)
 Plasma volume
○ Increased by 50% ( appx 1.2 litres)
 RBC volume
○ Increased by 20 – 30 % ( appx 250 – 400 ml)
Increased cardiac output
 Increased by 40 – 50% ( appx 1.8 litres / min)

5. Haemodynamic changes
• Decreased peripheral vascular resistance
– Decreased by 20 – 25%
• Decreased pulmonary vascular resistance
– Decreased by 30 – 35%
• Decreased colloid oncotic pressure
– Decreased by 10 – 15% from 20.8 mm of Hg to 18 mm of Hg
• Increased heart rate
– Increased by 15 – 20%
• Increased regional blood flow
– Uterine 750 ml /min ; Renal 1200 ml / min ; Cutaneous 500ml /
min

6. Clinical Implications
• Increased cardiac workload
• Misinterpretation as heart disease
• Aggravation of pre-existing disease
• Susceptibility to Pulmonary edema
– Pre eclampsia
– Heart disease

7. Symptoms & Signs which mimic Heart
disease during pregnancy
• Breathlessness
• Pedal oedema
• Easy fatigability
• Palpitations
• Orthopnoea
• Soft systolic murmurs
• Continuous parasternal murmurs
• Third heart sound
• Displacement of the heart

8. Effects of pregnancy on heart disease
• Precipitation of cardiac failure
– Aggravating factors
• Maternal age
• Arrhythmias
• Anaemia
• Pre eclampsia
• Multifetal gestation
• Activity
• Infection
• Anxiety
• Increased coagulability of blood
• Risk of infective endocarditis during labour / termination of pregnancy

9. Haematologic changes
• Physiologic haemodilution
• Neutrophilia
• Marked leukocytosis in labour
• ESR ↑
• Complement C3 and C4 elevated significantly
• Increased clotting factors ( V, VII,VIII, IX, X, XII and Fibrinogen)
• Impaired fibrinolysis through increase in Plasminogen activator
inhibitors 1 and 2 (PAI-1/ PAI-2)
• Increased platelet size

10. Clinical implications
• Increased demands during pregnancy unmask
iron and folic acid deficiency states, and
haematologic disorders like
haemoglobinopathies
• Pregnancy and puerperium are thrombogenic
states

11. Metabolic changes
• Water retention approx 6.5 litres
• Increased plasma lipids and lipoproteins
– Serum cholestrol ↑ 40%
– Serum triglycerides ↑ 50%
• Altered plasma proteins
– Albumin ↓ to ~ 3 gm% (Non pregnant ~ 4.3 gm%)
– Globulin ↑ to ~ 3 gm% (Non pregnant ~ 2.6 gm%)
– A:G ratio 1 : 1 (Non pregnant 1.7 : 1)
• Altered pH
– 7.45 (Non pregnant 7.4)
• Altered plasma bicarbonate
– 22 m mol /L (Non pregnant 26 m mol /L)

12. Respiratory system
• Increased awareness of a desire to breathe
(Progesterone induced central effect)
• Diaphragm rises by ~ 4 cm. Transverse diameter
of thoracic cage ↑ by ~ 2 cm
• Functional residual capacity ↓ to ~ 1500 ml (Non
pregnant ~ 2000 ml)
• Respiratory rate unchanged
• ↑ tidal volume ~ 700 ml (Non pregnant ~ 500ml)
• 40 % ↑ minute ventilation ~ 10.5 L (Non
pregnant 7.5 L)
• Respiratory alkalosis pCO ~ 28 mm Hg (Non

13. Clinical implications
• Increased awareness of desire to breathe may be
mistaken for dyspnoea
• Respiratory adaptations help in meeting oxygen
requirements of the fetus
• Respiratory alkalosis present in pregnancy
• ↑ 2,3 – DPG levels in maternal erythrocytes shifts
Oxygen Dissociation Curve to the right, counter-
acting the effect of respiratory alkalosis and
facilitating oxygen transfer to the fetus
• ABG values need to be interpreted in the context
of pregnancy

14. Urinary system
• Dilatation of renal pelvis, calyces and ureters
because of hormonal and mechanical
influences
• GFR ↑ 50% (Non pregnant 120 ml / min)
• Renal plasma flow ↑ 45 – 50%
• ↓ Serum creatinine & Blood urea levels
• Serum osmolality ↓ by ~ 10 m Osm / Kg (Non
pregnant 280 – 300 m Osm / Kg)

15. Clinical implications
• Hydronephrosis and hydroureter during pregnancy
should not be mistaken for obstructive uropathy
– These changes are more marked on the right side
– These changes may take upto 12 weeks to resolve post-
partum)
• Upper UTIs are more virulent
• Nocturia more likely as dependant edema fluid is
mobilized and excreted by the kidney
• ↑ frequency due to mechanical bladder
compression
• S. creatinine > 0.8 mg% and Blood urea > 30 mg%

16. Gastro – intestinal system
• Displacement of organs
– Appendix displaced upwards and laterally
• ↓ gastric empyting
• ↓ tone of gastro-esophageal sphincter
• Delayed intestinal transit time
• Altered liver function tests
– ↑ alkaline phosphatase (Non pregnant 21 – 91 IU/L
or 4 – 13 KA units)
– ↓ plasma albumin
– ↑ plasma globulin
• Hyperemia and softening of gums

17. Clinical implications
• Atypical symptoms and signs of appendicitis
during pregnancy. Risk of peritonitis ↑
• Major risk of regurgitation and acid aspiration
during GA
• ↑ incidence of reflux oesophagitis,
constipation and haemmorhoids during
pregnancy
• Bleeding from gums during pregnancy while
brushing

18. Endocrine system
• ↑ serum Prolactin ~ 150 ng / ml (Non pregnant
< 20 ng / ml)
• ↑ TBG
• ↑ Total T3 (Non pregnant 80 -100 ng / dl) and
T4 (Non pregnant 4 -12 μgm /dl)
• TSH levels unchanged except for slight decrease
in I trimester ( normal range < 5 μIU/ml or < 5
mIU / L)
• ↑ BMR by 25 % can be attributed to fetal

19. Thank you