Physiological changes in pregnancy result in profound anatomical, physiological, and biochemical adaptations throughout a woman's body to support the growth of the fetus. These changes include increased blood volume, cardiac output, and blood flow to key organs. Respiratory function also adapts with increased tidal volume and minute ventilation. While these changes are normal and vital for a healthy pregnancy, they can also mimic or worsen underlying health conditions. It is important for healthcare providers to understand these adaptations in order to avoid misinterpreting them as signs of disease during 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