Modified WHO Classification of Maternal Cardiac Risk
On this page
Direct answer
The modified WHO (mWHO) classification grades the risk of maternal death and serious cardiac events in pregnancy into four classes, from class I, with no detectable increased risk, to class IV, where pregnancy carries an extremely high risk and is contraindicated. Class IV lesions include pulmonary arterial hypertension and severe left ventricular dysfunction. Women in classes III and IV need tertiary cardiac and obstetric care.
What you must remember
- Class I: no detectable increased risk; examples include a small patent ductus arteriosus, mitral valve prolapse, mild pulmonary stenosis and successfully repaired simple lesions.
- Class II: a small increase in maternal mortality or a moderate increase in morbidity, with examples such as unrepaired septal defects and repaired tetralogy with good function.
- Class II to III: an intermediate risk that is decided case by case, depending on the lesion and the haemodynamics.
- Class III: a significant increase in risk, with moderate left ventricular impairment as a typical example, needing expert care.
- Class IV: an extremely high risk, where pregnancy is contraindicated; examples include pulmonary arterial hypertension, Eisenmenger syndrome and severe left ventricular dysfunction.
- Assessment: the grade depends on the lesion, residual haemodynamics and ventricular function, not on the diagnosis name alone.
Mapping each class to care
The mWHO grade is assigned from the lesion, its residual haemodynamics and the ventricular function, so the same diagnosis can fall into different classes. Each class maps to a level of care and a counselling message.
| Class | Risk | Example lesions | Care setting |
|---|---|---|---|
| I | No detectable increase | Small PDA, mitral valve prolapse, mild pulmonary stenosis; repaired simple lesions | Routine obstetric care with review |
| II | Small increase | Unrepaired septal defects; repaired tetralogy | Cardiology input during pregnancy |
| II to III | Intermediate, case by case | Varies with lesion and function | Cardiology review at each stage |
| III | Significant increase | Moderate left ventricular impairment | Tertiary centre with cardiology and obstetrics |
| IV | Extremely high; contraindicated | Pulmonary arterial hypertension, Eisenmenger, severe LV dysfunction | Pre-pregnancy counselling, including termination |
A class IV grade means pregnancy should not be undertaken, so counselling before conception carries the greatest weight. Classes III and IV are managed in a tertiary centre, and intermediate cases are reviewed at each stage of pregnancy.
Where the exam tries to catch you
Vignettes describe a cardiac diagnosis and ask for the class, then test the traps around repaired lesions and pulmonary hypertension.
- Trap: reading mWHO as a survival score. Correct: it grades the risk of maternal death and serious cardiac events, so it is a risk category rather than a prognosis for one patient.
- Trap: assuming repaired lesions always belong to class I. Correct: residual lesions, arrhythmias and ventricular function can move a repaired heart to a higher class.
- Trap: counselling that pregnancy is safe in pulmonary arterial hypertension. Correct: PAH is class IV, so pregnancy is contraindicated and counselling must cover termination options.
- Trap: assigning a class without assessing ventricular function. Correct: ventricular function is central to the grade, so echocardiography is essential.
Frequently asked questions
What is the highest mWHO class in maternal cardiac risk?
Class IV is the highest mWHO class in maternal cardiac risk, and pregnancy is contraindicated in it. Pulmonary arterial hypertension, Eisenmenger syndrome and severe left ventricular dysfunction are examples of class IV conditions.
Which conditions are examples of mWHO class I?
A small patent ductus arteriosus, mitral valve prolapse, mild pulmonary stenosis and successfully repaired simple lesions are examples of mWHO class I. These carry no detectable increased risk of maternal death or serious cardiac events in pregnancy.
Why is ventricular function important in the mWHO classification?
Ventricular function is central to the mWHO classification because moderate or severe left ventricular impairment moves a patient into class III or IV. Echocardiography is therefore essential before any counselling about pregnancy.
What does a class IV grade mean for pregnancy counselling?
A class IV grade means pregnancy is contraindicated because the risk of maternal death is extremely high. Counselling should cover contraception, pre-pregnancy options and termination permitted under the MTP Act to protect the mother's health.