WHO (Modified) Classification of Pregnancy with Heart Disease

Principles of the Classification

Application: Conditions by Class

mWHO Class I - No detectable increased risk

• Uncomplicated, small, or mild pulmonary stenosis / mitral valve prolapse
• Successfully repaired simple lesions (ASD, VSD, PDA, anomalous pulmonary venous drainage)
• Isolated atrial or ventricular ectopic beats

mWHO Class II - Small increased risk

• Unoperated ASD or VSD
• Repaired tetralogy of Fallot
• Most supraventricular arrhythmias
• Turner syndrome without aortic dilation
• NYHA class I-II with good ventricular function

mWHO Class III - Significantly increased risk (expert center required)

• Mild left ventricular impairment (EF < 45%)
• Hypertrophic cardiomyopathy
• Native or tissue valve disease not in Class I or IV (e.g., mild mitral stenosis, moderate aortic stenosis)
• Marfan or other heritable thoracic aortic disease (HTAD) without aortic dilation
• Aorta < 45 mm in bicuspid aortic valve pathology
• Repaired cyanotic heart disease
• Moderate left ventricular impairment (EF 30-45%)
• Mechanical valve
• Systemic right ventricular impairment (mild-moderate)
• Fontan circulation (uncomplicated)
• Moderate mitral stenosis
• Severe asymptomatic aortic stenosis
• Moderate aortic dilation (40-45 mm in Marfan/HTAD; 45-50 mm in bicuspid AV)

mWHO Class IV - Pregnancy contraindicated

• Pulmonary arterial hypertension (any cause) - maternal mortality up to 50%
• Severe systemic ventricular dysfunction (EF < 30% or NYHA class III-IV)
• Previous peripartum cardiomyopathy with any residual LV impairment
• Severe mitral stenosis
• Severe symptomatic aortic stenosis
• Systemic right ventricle with moderate or severely decreased function
• Severe aortic dilation: > 45 mm in Marfan/HTAD, > 50 mm in bicuspid AV, Turner syndrome ASI < 25 mm/m²; tetralogy of Fallot > 50 mm
• Severe coarctation of the aorta
• Fontan with any complication
• Vascular Ehlers-Danlos

Maternal Cardiac Event Rates by Class

Key Clinical Points

1. Class IV conditions warrant pre-pregnancy counseling and, if pregnancy occurs, early discussion of termination given prohibitive risk.
2. Class III and IV patients must be managed by a multidisciplinary team - cardiologist, maternal-fetal medicine specialist, anesthesia, and often cardiac surgery.
3. Maternal and neonatal adverse events correlate - cyanotic heart disease increases miscarriage risk and neonatal complications.
4. CARPREG II scoring (published more recently) supplements WHO class by adding 10 predictors including process-of-care factors (e.g., late presentation to prenatal care), achieving a c-statistic of 0.77.
5. For most pregnant women with heart disease, vaginal delivery is recommended unless obstetric or specific cardiac indications exist.