29th June 2023

Cardiovascular

From the early stages, there is a drop in peripheral vascular resistance linked to peripheral vasodilation. Cardiac output increases by about 40% to compensate for this. Much of this increase is due to increased stroke volume, however, heart rate also increases by 10-15bpm.

The fall in peripheral vascular resistance leads to a drop in blood pressure (BP) in the first 20 weeks of pregnancy before rising to pre-pregnancy levels by term. There may be an overshoot for the first few days postpartum before settling to pre-pregnancy levels.

There is also a significant drop in serum colloid osmotic pressure with no change in pulmonary capillary wedge pressure.

Changes in stroke volume can lead to changes in examination and ECG during normal pregnancy; an ejection systolic murmur is very common, as is a loud first heart sound and an audible third heart sound. Ectopic beats, a small Q wave and an inverted T wave in lead III can be normal, as can ST depression and T wave inversion in inferior and lateral leads. The axis shifts to the left, which can also be seen on CXR, where there is an increase in cardiothoracic ratio.