When during pregnancy does blood volume increase? can this cause a pregnancy heart murmur?

2nd trimester: Most of the blood volume changes occur during the second trimester and continue until 34-36 weeks. Along with blood volume increases, there is a rise in cardiac output. With the rise in cardiac output, the presence of a heart murmur is common. Heart murmur does not necessarily indicate the presence of heart disease, and most pregnant women with a heart murmur have a normal heart.