When should the risk tolerance of modified World Health Organization (WHO) maternal cardiovascular risk be used in women with pre-existing cardiovascular conditions, such as heart disease or hypertension, who are pregnant or planning pregnancy?

When to Use Modified WHO Maternal Cardiovascular Risk Classification

The modified WHO maternal cardiovascular risk classification should be used for all women of childbearing age with known cardiac disease during routine contraception review, formal pre-conception counseling, and throughout pregnancy to guide frequency of monitoring and multidisciplinary care planning. 1

Primary Clinical Applications

Pre-Conception Risk Stratification

• Routine assessment of pregnancy risk should be part of standard care for all women with cardiac disease who are of childbearing age, regardless of whether they are currently planning pregnancy 1
• The modified WHO classification must be applied during formal pre-conception counseling to allow for medical optimization and replacement of teratogenic medications before conception 1
• This classification integrates all known maternal cardiovascular risk factors including the underlying heart disease and any other co-morbidity, making it more comprehensive than statistically-derived scores like CARPREG or ZAHARA 1

Determining Need for Specialized Care

• Women at moderate to high risk (modified WHO score 2-3 and 4) require assessment by a multidisciplinary pregnancy heart team including cardiologist, obstetrician, and anesthetist at a specialist center 1
• The European Society of Cardiology Task Force specifically recommends maternal risk assessment be carried out according to the modified WHO risk classification because it includes contraindications for pregnancy not incorporated in other risk scores 1

Risk-Based Monitoring Algorithms

WHO Class I (2.5-5% maternal risk)

• Conditions include uncomplicated small/mild pulmonary stenosis, patent ductus arteriosus, mitral valve prolapse, and successfully repaired simple lesions 1
• Cardiology follow-up may be limited to one or two visits during pregnancy 1

WHO Class II (5.7-10.5% maternal risk)

• Includes unrepaired atrial or ventricular septal defect, repaired tetralogy of Fallot, and most arrhythmias 1
• Follow-up every trimester is recommended 1

WHO Class II-III (10-19% maternal risk)

• Encompasses mild left ventricular impairment (LVEF >45%), hypertrophic cardiomyopathy, Marfan syndrome without aortic dilation, and native/tissue valvular disease 1
• Risk varies by individual patient factors requiring expert assessment 1

WHO Class III (19-27% maternal risk)

• Includes mechanical valves, moderate left ventricular impairment (LVEF 30-45%), Fontan circulation, unrepaired cyanotic heart disease, and aortic dilation 40-45mm in Marfan syndrome 1
• Frequent (monthly or bimonthly) cardiology and obstetric review during pregnancy is required 1
• Pregnancy should be carefully considered in these patients, particularly those who are anticoagulated 1

WHO Class IV (40-100% maternal risk)

• Pregnancy is contraindicated in conditions including pulmonary arterial hypertension, severe systemic ventricular dysfunction (LVEF <30%, NYHA III-IV), severe mitral/aortic stenosis, Marfan syndrome with aorta >45mm, and previous peripartum cardiomyopathy with residual impairment 1, 2
• If pregnancy occurs despite counseling, termination should be discussed; if pregnancy continues, monthly or bimonthly review is needed 1
• Maternal mortality in pulmonary arterial hypertension ranges from 30-50%, making it the highest risk cardiac condition in pregnancy 2

Validation and Clinical Utility

• The modified WHO classification has been validated to predict not only maternal cardiovascular events (occurring in 4.2%, 15.0%, 25.0%, and 56.4% in classes I, II, III, and IV respectively) but also adverse fetal outcomes including preterm delivery, low birth weight, and NICU admission 3
• All maternal mortality in validation studies occurred exclusively in WHO Class IV patients 3
• Recent single-center data confirms that even with specialized multidisciplinary care, cardiovascular events occur in 65.6% of WHO Class IV pregnancies, with substantial long-term morbidity 4

Critical Advantages Over Alternative Scores

The modified WHO classification should be preferred over CARPREG and ZAHARA scores because it includes absolute contraindications to pregnancy (such as pulmonary arterial hypertension and dilated aorta) that were under-represented in those statistically-derived studies 1

Essential Pitfalls to Avoid

• Do not rely solely on the classification number without considering individual patient factors and disease progression 5
• Recognize that guidance for pregnancies following assisted reproduction remains lacking, despite rising mortality in this population (6 of 82 cardiac deaths in recent UK data) 1
• Remember that only 22% of women who died from cardiac causes during pregnancy had known pre-existing cardiac problems, emphasizing the need for vigilance even in apparently low-risk patients 1
• The classification must be reassessed at regular intervals during pregnancy, not just at initial evaluation, as hemodynamic changes can alter risk 5, 6