Physiology: Cardiovascular changes
during pregnancy
Significant cardiovascular and haemodynamic
changes occur early in pregnancy in order to provide
enough blood for the embryo and maintain normal
fetal intrauterine growth. Such changes include increased
maternal plasma volume, cardiac output and
heart rate, and decreased maternal systemic vascular
resistance and arterial blood pressure.46
The expansion of maternal plasma volume is due
to stimulation of the renin-angiotensin-aldosterone
system. As a compensatory mechanism, vasodilator
synthesis is increased in order to maintain normotension.
47 Such vasodilators include the kallikrein-kinin
system, prostacyclin, nitric oxide and vascular-endothelial
growth factor (VEGF).48-50
In addition to the functional adaptation of the maternal
cardiovascular system, structural changes also
occur during pregnancy. This adaptive remodelling
results in cardiac hypertrophy that enables the heart
to cope with the increased demands of gestation. This
hypertrophy is reversible and is not associated with
long-term cardiovascular dysfunction.51
In summary, haemodynamic changes during pregnancy
include a reduction of systolic, diastolic and
mean arterial blood pressure in the second trimester
followed by a slight increase in the third, a reduction
of total vascular resistance, especially in the second
trimester, and an increase of cardiac output