What is considered a normal ejection fraction (EF) in a pregnant woman?

Normal Ejection Fraction in Pregnancy

A normal ejection fraction during pregnancy ranges from 50% to 70%, which is identical to the reference range for non-pregnant women. 1

Standard Reference Values

• The normal EF range of 50-70% applies throughout all trimesters of pregnancy, as pregnancy does not fundamentally alter what constitutes a normal ejection fraction measurement 1

• The European Society of Cardiology establishes the normal range using the biplane method of discs at 53-73% (mean 63 ± 5%), which remains the standard regardless of pregnancy status 2

Physiological Context During Pregnancy

While the normal EF range remains unchanged, it's important to understand the hemodynamic adaptations that occur:

• Cardiac output increases by 30-50% during pregnancy through increased stroke volume and elevated heart rate (15-20 bpm above baseline), but this occurs while maintaining normal ejection fraction 1

• Systemic vascular resistance decreases due to endogenous vasodilators, reaching its lowest point in the second trimester 1

• Heart rate typically increases to 80-95 beats per minute during early second trimester 1

Clinical Significance of Reduced EF in Pregnancy

An ejection fraction below 40% is considered reduced and represents a significant predictor of maternal cardiovascular events during pregnancy. 3, 1

High-Risk Thresholds

• Women with EF <40% should be counseled against pregnancy due to substantially increased risk of complications 3, 1

• EF <30% represents very high risk, with significantly worse fetal and neonatal outcomes, and these patients require intensive counseling about poor obstetrical outcomes 4, 5

• EF <20% is considered a contraindication to pregnancy unless improved under treatment 4

Risk Stratification

The modified WHO risk classification uses EF thresholds for pregnancy risk assessment:

• EF ≥50%: Standard prenatal cardiac monitoring is generally sufficient 1

• EF 40-49% (borderline/mildly reduced): Requires more frequent monitoring during pregnancy 1

• EF <40%: High-risk category requiring frequent echocardiographic surveillance every 4-8 weeks to assess for deterioration 3, 1

Monitoring Recommendations by EF Category

For women with normal EF (50-70%):

• Standard prenatal cardiac monitoring is appropriate 1
• No specific cardiac intervention or activity restriction is warranted based on EF alone 2

For women with mildly reduced EF (40-49%):

• More frequent cardiac monitoring throughout pregnancy 1
• Serial echocardiographic assessments to detect deterioration 1

For women with reduced EF (<40%):

• Frequent echocardiographic surveillance every 4-8 weeks 3, 1
• Joint cardiac and obstetric care in a specialist unit 3
• Consideration of therapeutic anticoagulation due to increased thromboembolic risk 3

Important Caveats and Pitfalls

Measurement variability is a critical consideration:

• EF measurements can vary between imaging modalities (echocardiography, MRI, nuclear imaging) and between interpreters 1, 2
• When reporting EF as a numerical value, always specify the imaging modality and method of analysis 1
• A single EF measurement may not be adequate, particularly for borderline values (41-49%) 2

Load dependency affects interpretation:

• EF is load-dependent and cannot distinguish between preload, afterload, and intrinsic contractility 2
• Volume status (hypovolemia/dehydration) can artificially elevate EF 2
• Small ventricular cavity may produce artificially high EF calculations (>70%) 2

Subclinical dysfunction may be present despite normal EF:

• Women who later develop peripartum cardiomyopathy (PPCM) have been shown to have normal EF during pregnancy (60% ± 6.6%) but abnormal systolic strain on advanced imaging 6
• Consider global longitudinal strain (GLS) assessment if clinical suspicion of dysfunction exists despite preserved EF, with normal values being more negative than -16% 2

Peripartum Cardiomyopathy Considerations

PPCM typically presents with severely reduced EF in the peripartum period:

• Most PPCM patients present peri- or post-partum with acute deterioration 3
• Anticoagulation should be considered in PPCM patients with very low EF due to frequent peripheral and cerebral embolism 3
• When EF has not normalized after PPCM, subsequent pregnancy should be strongly discouraged due to 30-50% recurrence risk 3