Maternal Cardiovascular Risk Stratification: WHO Classification and CARPREG II Scoring
Women at highest maternal cardiovascular risk are those with WHO Class IV conditions—including pulmonary arterial hypertension, severe ventricular dysfunction (LVEF <30%), severe valve stenosis, and significantly dilated aortas—where pregnancy is contraindicated due to extremely high mortality risk. 1
WHO Risk Classification System
The modified WHO classification stratifies maternal cardiovascular risk into four categories based on mortality and morbidity outcomes: 1
WHO Class I (Minimal Risk)
- No detectable increased maternal mortality; no or mild morbidity increase 1
- Includes uncomplicated mild pulmonary stenosis, small patent ductus arteriosus, successfully repaired simple lesions (ASD, VSD), and isolated ectopic beats 1
- Cardiology follow-up limited to 1-2 visits during pregnancy 1
WHO Class II (Low-Moderate Risk)
- Small increased maternal mortality or moderate morbidity increase 1
- Includes unoperated ASD/VSD, repaired tetralogy of Fallot, and most arrhythmias if otherwise uncomplicated 1
- Requires cardiology follow-up every trimester 1
WHO Class II-III (Variable Risk)
- Risk depends on individual clinical factors 1
- Includes mild LV impairment, hypertrophic cardiomyopathy, native/tissue valve disease (not Class I or IV), Marfan syndrome without aortic dilatation, aorta <45mm with bicuspid aortic valve, and repaired coarctation 1
WHO Class III (High Risk)
- Significantly increased maternal mortality or severe morbidity; expert counseling required 1
- Includes mechanical valves, systemic right ventricle, Fontan circulation, unrepaired cyanotic heart disease, complex congenital heart disease, aortic dilatation 40-45mm in Marfan syndrome, and aortic dilatation 45-50mm with bicuspid aortic valve 1
- Requires monthly or bimonthly cardiology and obstetric review 1
WHO Class IV (Pregnancy Contraindicated)
- Extremely high maternal mortality or severe morbidity risk 1
- If pregnancy occurs, termination should be discussed; if continued, manage as Class III 1
Specific WHO Class IV conditions include: 1
- Pulmonary arterial hypertension of any cause
- Severe systemic ventricular dysfunction (LVEF <30%, NYHA III-IV)
- Previous peripartum cardiomyopathy with any residual LV impairment
- Severe mitral stenosis or severe symptomatic aortic stenosis
- Marfan syndrome with aorta >45mm
- Aortic dilatation >50mm with bicuspid aortic valve
- Native severe coarctation
CARPREG II Risk Score
The CARPREG II score demonstrates superior predictive accuracy compared to the original CARPREG and modified WHO classification, incorporating 10 predictors across three domains. 2, 3
Five General Predictors: 2, 3
- Prior cardiac events or arrhythmias
- Poor functional class (NYHA III-IV) or cyanosis
- High-risk valve disease or left ventricular outflow tract obstruction
- Systemic ventricular dysfunction
- No prior cardiac interventions
Four Lesion-Specific Predictors: 2, 3
- Mechanical heart valves
- High-risk aortopathies
- Pulmonary hypertension
- Coronary artery disease
One Delivery of Care Predictor: 2, 3
- Late pregnancy assessment (lack of early cardiology evaluation)
The CARPREG II score calculates individualized risk percentages for maternal cardiovascular complications, with cardiac events occurring in approximately 16% of pregnancies overall in the derivation cohort. 3 Recent validation studies demonstrate CARPREG II has the highest discriminatory power (AUC 0.774-0.782) compared to modified WHO (AUC 0.697-0.754) and ZAHARA (AUC 0.604-0.685). 4, 5, 6
Clinical Application Algorithm
For all women with known or suspected cardiovascular disease: 1
Pre-pregnancy counseling by cardiology experts is mandatory for adolescents when sexually active and all women considering pregnancy 1
Apply both WHO classification and CARPREG II scoring to stratify risk, as CARPREG II provides superior predictive accuracy while WHO classification identifies absolute contraindications not captured by CARPREG 2, 4, 5
High-risk patients (WHO III-IV or high CARPREG II scores) require multidisciplinary team management in specialist centers with joint cardiology-obstetric care from early pregnancy 1
Review and optimize medications pre-pregnancy, discontinuing teratogenic agents 1
Hospital delivery is advised for all women with heart disease 1
Critical Pitfalls
The CARPREG and ZAHARA scores are population-dependent and underrepresent critical conditions like pulmonary arterial hypertension and dilated aorta, which were excluded from derivation cohorts. 1 Therefore, these absolute contraindications must be identified through WHO classification regardless of calculated scores. 1
CARPREG II demonstrates better performance in congenital heart disease (AUC 0.768) than acquired disease (AUC 0.677), while modified WHO performs comparably across both populations. 4 For inherited cardiomyopathies specifically, CARPREG II shows the highest predictive accuracy (AUC 0.782). 5
Neonatal complications occur in 20-28% of pregnancies with maternal heart disease, emphasizing that risk extends beyond maternal outcomes alone. 1