Modified WHO Classification of Maternal Cardiovascular Risk

Definition

The modified WHO (mWHO) classification is the primary prospectively validated risk stratification tool for estimating maternal cardiovascular risk in women with heart disease who are pregnant or contemplating pregnancy. It assigns patients to one of four risk classes (I, II, II–III, III, IV) based on the underlying cardiac diagnosis, with class IV representing conditions where pregnancy is contraindicated due to 40–100% cardiac event rates.

Key Concepts

Risk Class Definitions and Event Rates

• Class I (2.5–5% cardiac event rate): Uncomplicated or mild PS; repaired simple lesions (small ASD/VSD, repaired PDA, isolated ectopics/supraventricular ectopics); no detectable increased maternal risk sources/cv-pregnancy-esc-2018 (rating: very high)
• Class II (5.7–10.5%): Unoperated ASD or VSD; repaired tetralogy of Fallot; arrhythmias not Class I; mild LV impairment; HCM; non-severe native or bioprosthetic valve disease not Class I or IV; Marfan without aortic dilatation; aorta <45 mm in BAV sources/cv-pregnancy-esc-2018
• Class II–III (10–19%): Mild LV impairment; HCM; non-severe native or bioprosthetic valve disease not Class I or IV; moderate valve disease not classified I or IV; uncomplicated mild-moderate systemic ventricular dysfunction (EF 30–45%) sources/cv-pregnancy-esc-2018
• Class III (19–27%): Mechanical valve prosthesis; systemic RV (Mustard/Senning TGA or congenitally corrected TGA); Fontan circulation without complications; unrepaired cyanotic CHD (not mWHO IV); other complex CHD; moderate LVOTO; moderate systemic ventricular dysfunction (EF 30–45%) sources/cv-pregnancy-esc-2018
• Class IV (40–100% — pregnancy not recommended/contraindicated): — see below sources/cv-pregnancy-esc-2018

mWHO Class IV Conditions (Contraindicated Pregnancies)

• Pulmonary arterial hypertension (PAH) of any cause
• Severe systemic ventricular dysfunction (LVEF <30%, or NYHA class III–IV)
• Previous peripartum cardiomyopathy with any residual LV impairment (even mild; not full recovery)
• Severe mitral stenosis (MS) (valve area <1.0 cm²)
• Severe symptomatic aortic stenosis (AS)
• Systemic right ventricle with moderate or severe dysfunction (Mustard/Senning/congenitally corrected TGA)
• Severe aortic dilatation:

  • 45 mm in Marfan syndrome or Loeys-Dietz syndrome

  • 50 mm in bicuspid aortic valve (BAV) disease

• Vascular Ehlers-Danlos syndrome
• Severe re-coarctation of the aorta
• Fontan circulation with any complication (saturations <85%, depressed ventricular function, moderate-severe AV regurgitation, refractory arrhythmia, protein-losing enteropathy)

Prospective Validation

• mWHO classification is the only prospectively validated maternal cardiac risk tool; validated in the ROPAC (Registry of Pregnancy and Cardiac Disease) and ZAHARA studies sources/cv-pregnancy-aha-2020 (rating: high); sources/cv-pregnancy-esc-2018 (rating: very high)
• All validated risk models include: prior CVD event, arrhythmia history, prior HF, poor functional class (NYHA), resting cyanosis, anticoagulant use, and mechanical valve presence
• Other risk models (CARPREG, ZAHARA scores) have not been prospectively validated and are used as supplementary tools

Application in Practice

• Risk assessment recommended for all women with known or suspected CVD of childbearing age, both before and after conception (IC) sources/cv-pregnancy-esc-2018
• High-risk patients (mWHO III–IV) should be managed by a multidisciplinary pregnancy heart team at specialised centres
• mWHO classification also guides contraception decisions: mWHO IV is a contraindication to pregnancy → discuss effective contraception (IUD or progestin implant preferred)
• IVF: contraindicated in mWHO IV; high risk in mWHO III (natural cycle IVF preferred to avoid superovulation thrombotic risk)
• Surveillance intensity: Class I/II — two or three visits per pregnancy; Class III — monthly; Class IV — individualised intensive with specialist teams

Predictors of Adverse Cardiac Events in Pregnancy

• NT-proBNP >128 pg/mL at 20 weeks gestation → independent predictor of later cardiac events sources/cv-pregnancy-esc-2018
• CARPREG II score integrates: prior cardiac event/arrhythmia, NYHA II–IV or cyanosis, mechanical valve, ventricular dysfunction, high-risk lesion, emergent CS, late pregnancy visit
• NT-proBNP and other biomarkers added to risk prediction in 2018 vs. 2011 guidelines

Contradictions / Open Questions

• mWHO IV threshold for PPCM is contentious: "any residual LV impairment" is strict — some centres consider repeat pregnancy in women with near-normal EF recovery (50–55%) with intensive monitoring, despite guideline discouragement sources/cv-pregnancy-esc-2018
• mWHO classification does not account for the severity of PAH therapy; patients on combination oral PAH therapy may have better outcomes than historically reported 16–30% mortality rates with targeted therapy
• The mWHO II–III category boundary is not sharply defined and inter-observer variation exists in categorising mild-moderate lesions
• Validated primarily in European/high-income country populations; applicability to diverse global populations and lower-resource settings uncertain sources/cv-pregnancy-aha-2020

Connections

• Related to concepts/Cardio-Obstetrics — mWHO is the central tool of the pregnancy heart team
• Related to entities/Peripartum-Cardiomyopathy — prior PPCM with any residual LV dysfunction = mWHO IV
• Related to concepts/Hypertensive-Disorders-of-Pregnancy — pre-eclampsia and gestational HTN influence subsequent mWHO assessment
• Related to entities/Pulmonary-Hypertension — PAH is the prototypical mWHO IV condition
• Related to concepts/Eisenmenger-Syndrome — mWHO IV (severe PH with right-to-left shunt)
• Related to concepts/Fontan-Circulation — mWHO III (uncomplicated) or IV (complicated)

Sources

• sources/cv-pregnancy-esc-2018
• sources/cv-pregnancy-aha-2020