What type of heart murmur is most common in pregnancy?

Heart Murmurs in Pregnancy

A soft grade 1-2 midsystolic murmur heard along the mid to upper left sternal edge is the most common type of heart murmur in pregnancy. 1, 2

Physiological Basis for Murmurs in Pregnancy

The cardiovascular system undergoes significant adaptations during pregnancy that contribute to the development of heart murmurs:

• 50% increase in circulating blood volume
• Commensurate increase in cardiac output (peaks between mid-second and third trimesters)
• Increase in stroke volume
• Increase in heart rate (10-20 beats per minute)
• Decreased systemic vascular resistance 1

These hemodynamic changes create the perfect conditions for the development of flow murmurs, particularly midsystolic murmurs.

Characteristics of Normal Pregnancy Murmurs

Midsystolic Murmur

• Location: Mid to upper left sternal edge
• Intensity: Soft (grade 1-2/6)
• Timing: Midsystolic (begins after S1, ends before S2)
• Configuration: Often crescendo-decrescendo 1, 2

Other Normal Cardiovascular Findings in Pregnancy

• Hyperkinetic precordial impulse
• Louder first heart sound with prominent splitting
• Physiologically split second heart sound (may widen or appear fixed in later stages)
• Third heart sounds in most pregnant women 1, 2

Continuous Murmurs in Pregnancy

Two types of continuous murmurs may also be heard during pregnancy:

1. Cervical venous hum:

   • Best appreciated in right supraclavicular fossa
   • Can be obliterated by movement of chin toward stethoscope
   • Can be eliminated by digital pressure over ipsilateral jugular vein 1, 2

2. Mammary souffle:

   • Located over engorged breast
   • Can be eliminated with firm pressure on stethoscope diaphragm
   • Heard in supine position, attenuates or disappears when standing
   • Most common in late pregnancy or early puerperium 1, 2

Effect of Pregnancy on Pathological Murmurs

• Stenotic valve lesions (e.g., mitral stenosis, aortic stenosis): Murmurs become accentuated due to increased blood volume and cardiac output
• Regurgitant lesions (e.g., aortic regurgitation, mitral regurgitation): Murmurs may attenuate or become inaudible due to lowered systemic vascular resistance 1

Clinical Implications

When to Reassure

• Isolated soft midsystolic murmur without other abnormal findings
• Normal physiologic S3, S4, or splitting without other abnormal findings 2

When to Investigate Further

• Diastolic murmurs (virtually always pathological)
• Loud (grade ≥3/6) systolic murmurs
• Murmurs associated with symptoms
• S3 with signs of heart failure 1, 2

Diagnostic Approach

Echocardiography is the diagnostic test of choice for evaluating heart murmurs during pregnancy when there is concern for pathology. However, in the absence of other clinical abnormalities, echocardiography may not be necessary for the assessment of soft midsystolic murmurs in pregnancy 3.

Pitfalls to Avoid

• Mistaking a normal physiologic murmur for pathological heart disease
• Overlooking pathological murmurs by attributing them to normal pregnancy changes
• Failing to recognize that diastolic murmurs are almost always pathological and require further evaluation
• Not considering patient position when evaluating murmurs (some murmurs like mammary souffle vary with position) 1, 2

Remember that while most systolic murmurs in pregnancy are benign, proper evaluation is essential to distinguish physiologic from pathologic murmurs, especially in women with known or suspected heart disease.