Table 2.

Physiological changes of the cardiovascular system during the pregnancy [28–38].

Feature	Change	Week of pregnancy/trimester
Blood volume	↑ 1-2 L (up to 40-50%)	Increase from 7th week, peaks at 30-34 weeks
Plasma volume	↑ By 30–50% (=1200-1600 mL) till 70% in twin pregnancies
Plasma colloid osmotic pressure	↓ Of 10–15%
Colloid osmotic pressure/pulmonary capillary wedge pressure gradient	↓ By 30%
Total body water content	↑ By 6.5-8 L
Red blood cells	↑ By 18-25%
Haematocrit	↓ To 32-34%
Platelet count	↓ By 20%	By term
PT, aPTT	Shortened	By term
Factors II and V, protein C	No change	By term
Fibrinogen, factors VII, VIII, IX, X, XII, and VWF	↑ More than 100%	By term
Factor XI	Variable	By term
Factor XIII, protein S	↓	By term
D-dimer	↑ Up to 400%	By term
Preload	↑
Afterload	↓
Cardiac output	↑ To 30-50%	From 6th week, peak between 16 and 28 weeks, decreases slightly from 30 weeks until labor
Stroke volume	↑ By 23-30%
SVR	↓ By 20%	Nadir at 20 week
	↑	Gradual rise after 20 weeks, till term
Heart rate	↑, Generally not above 100 beats/minute
Systolic blood pressure	=/↓ By 10-15 mmHg	In 1st trimester, returns to baseline in the second half of pregnancy
Diastolic blood pressure	↓ By 10-15 mmHg	Nadir at 28 week, returns to baseline in the second half of pregnancy
	↑	Gradual rise, till term
Pulmonary circulation	↑
Pulmonary capillary wedge pressure	=
Pulmonary vascular resistance	↓

Abbreviations: PT: prothrombine time; aPTT: activated partial prothrombine time; SVR: systemic vascular resistance.