Modified WHO Classification of Maternal Cardiovascular Risk in Pregnancy

Principles of the mWHO Classification

Application: Conditions Under Each Class

mWHO Class I (Maternal cardiac event rate: ~2.5-5.9%)

• Small/mild pulmonary stenosis
• Patent ductus arteriosus (uncomplicated)
• Mitral valve prolapse
• Successfully repaired simple lesions (ASD, VSD, PDA, anomalous pulmonary venous drainage)
• Isolated atrial or ventricular ectopic beats

mWHO Class II (Maternal cardiac event rate: ~5.7-10.5%)

• Unoperated ASD or VSD
• Repaired Tetralogy of Fallot
• Most supraventricular arrhythmias
• Turner syndrome without aortic dilation

mWHO Class III (Maternal cardiac event rate: ~10-19%)

• Mild left ventricular impairment (EF <45%)
• Hypertrophic cardiomyopathy
• Native or tissue valve disease not in WHO I or IV (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
• Mechanical valve
• Systemic right ventricular (mild to moderate) impairment
• Fontan circulation (uncomplicated)
• Unrepaired cyanotic heart disease
• Moderate mitral stenosis
• Moderate aortic dilation (40-45 mm in Marfan/HTAD; 45-50 mm in bicuspid aortic valve; Turner syndrome)
• Vascular Ehlers-Danlos

mWHO Class IV - Pregnancy Contraindicated (Maternal cardiac event rate: ~19-27%)

• Pulmonary arterial hypertension (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 aortic valve; tetralogy of Fallot >50 mm)
• Severe coarctation of the aorta
• Fontan with any complication

Follow-Up Frequency by Class

Key Points for Exam & Clinical Practice

1. mWHO IV = Pregnancy contraindicated - the "Big Three" to remember: pulmonary arterial hypertension, severe LV dysfunction (EF <30% or NYHA III-IV), and peripartum cardiomyopathy with residual LV impairment.
2. Mechanical valves = mWHO III (not IV) unless complicated - but carry very high anticoagulation management complexity.
3. Marfan syndrome risk depends on aortic root size: without dilation = mWHO III; with severe dilation (>45 mm) = mWHO IV.
4. ROPAC registry data confirmed that mWHO categories are strongly associated with maternal, obstetric, and fetal outcomes. Overall maternal death rate was ~1% in women with CVD, compared to 0.007% in the general population.
5. Other risk scores (CARPREG II, ZAHARA) provide similar predictive value but are more complex to apply. The mWHO system is preferred for clinical use.

Aortic Regurgitation (AR) & Mitral Regurgitation (MR) in Pregnancy

Core Principle

"The pregnancy-induced decrease in systemic vascular resistance reduces the risk of cardiac failure with these conditions, especially in those with chronic lesions."

• Harrison's Principles of Internal Medicine, 22nd Edition

Pathophysiology in Pregnancy

Mitral Regurgitation (MR) in Pregnancy

Etiology

• Young women: Rheumatic or congenital disease, mitral valve prolapse (MVP) (most common cause in developed countries)
• Older women: Hypertension, ischemia, idiopathic myocardial disease, infective endocarditis
• Rheumatic disease is the most common cause worldwide

Tolerance

• Mild to moderate MR: well tolerated - managed conservatively (reduced activity, salt restriction, low-dose diuretics if needed)
• Heart failure occurs in 20-25% of women with moderate to severe MR

WHO Classification

Management

• Mild/moderate: Reduced physical activity, salt restriction, diuretics (furosemide) if needed
• If already pregnant with severe MR: Maximum medical therapy; aim to carry to term; delay surgery if possible
• Diuresis + hydralazine + nitrates: First-line for heart failure in pregnancy (ACE inhibitors and ARBs are contraindicated)
• Surgical valve replacement: Avoid during pregnancy - high risk of fetal loss with cardiopulmonary bypass
• Valvuloplasty/repair: Best undertaken before pregnancy

MVP with MR

• MVP alone (without significant MR): mWHO I - pregnancy, labor, and delivery are safe
• MVP with significant MR: Treat as MR (higher risk class)

Aortic Regurgitation (AR) in Pregnancy

Etiology

• Rheumatic heart disease (often with coexisting mitral stenosis)
• Bicuspid aortic valve (BAV)
• Marfan syndrome (aortic annular dilation)
• Infective endocarditis
• Systemic lupus erythematosus (SLE)
• Coarctation of the aorta

Tolerance

• AR imposes a volume overload (not pressure overload) on the LV - generally well tolerated in pregnancy
• Both pregnancy and AR contribute to hypervolemia and peripheral vasodilation (synergistic effects)
• Chronic AR: prolonged course without decompensation; once heart failure appears, course may progress rapidly

Diagnosis

• High-pitched, blowing diastolic murmur
• Quantified by Doppler echocardiography

WHO Classification

Key Warning - Aortic Root/Dissection Risk

"Special care must be taken to rule out aortic aneurysm or dissection, especially if aortic regurgitation is associated with Marfan syndrome or coarctation of the aorta, because these conditions can result in aortic rupture and constitute strong reasons to advise against pregnancy."

• Creasy & Resnik's Maternal-Fetal Medicine

Management

• If LV dysfunction and heart failure absent: carefully supervised pregnancy is appropriate
• Aortic valve replacement needed: advise against pregnancy; complete family before cardiac dysfunction necessitates surgery
• Medical therapy in pregnancy: diuretics + hydralazine/nitrates (avoid ACE inhibitors/ARBs/ARNIs - teratogenic)
• Avoid surgical replacement during pregnancy

Side-by-Side Comparison: AR vs MR in Pregnancy

Postpartum Considerations (Both AR and MR)

• Women with regurgitant lesions are at increased risk for heart failure postpartum
• Mechanism: postpartum normalization of SVR in the face of a continued volume load
• Monitor closely; treat with diuretics if heart failure develops
• Women who develop AF during pregnancy are at high risk for embolic events - anticoagulation should be considered

Stages of Labour

STAGE 1 - Cervical Dilation

Two Phases:

Latent Phase

• Infrequent, irregular, moderately uncomfortable contractions
• Gradual cervical effacement (thinning), softening, and anterior repositioning
• Little active dilation occurs
• Duration: up to 20 hours (nullipara) | up to 14 hours (multipara)
• Best managed at home; clear liquids encouraged
• Prolonged latent phase: can be treated with morphine, which often accelerates transition to active phase

Active Phase

• Begins at 3-4 cm dilation
• Rapid, progressive cervical dilation
• Rate: ≥1.2 cm/hr (nullipara) | ≥1.5 cm/hr (multipara)
• Contractions become regular, stronger, and more frequent
• Fetal monitoring: fetal heart auscultation every 30 minutes (low-risk) or 15 minutes (high-risk)
• Depends on: strength/frequency of contractions + fetal head size and position + bony pelvis dimensions

STAGE 2 - Expulsion of the Fetus

• Average: 50-54 minutes (nullipara) | 20 minutes (multipara)
• Alert for possible CPD (cephalopelvic disproportion) if pushing >2 hrs (no epidural) or >3 hrs (with epidural) in nullipara
• Fetal heart auscultated every 15 minutes (low-risk) or 10 minutes (high-risk)

The 7 Cardinal Movements of Labour (Vertex/Cephalic Presentation)

"The fetus will follow the path of least resistance by adaptation of the smallest achievable diameter of the presenting part to the most favorable dimensions and contours of the birth canal."

• Roberts and Hedges' Clinical Procedures in Emergency Medicine

STAGE 3 - Placental Stage

• Duration: ~15 minutes in 90% of pregnancies
• Active intervention usually not needed until 30 minutes (unless hemorrhage)
• Retained placenta = not expelled within 60 minutes

Mechanism of Placental Separation

1. Uterus retracts - reduces area of placental attachment
2. Hematoma forms deep to placenta - separates it from uterine wall
3. Placenta separates through the spongy layer of decidua basalis
4. Expulsion through vaginal canal

Signs of Placental Separation

• Lengthening of the umbilical cord
• A gush of blood
• Change in contour of the uterine fundus (becomes globular and firm)

Management

• Allow spontaneous separation
• Gentle traction on cord + maternal expulsive efforts
• Oxytocin (20-40 units/L IV, or 20 units IM) to maintain uterine contractility
• Uterine massage + immediate breastfeeding aids uterine contraction

STAGE 4 - The Recovery Stage

• Monitor for: excessive vaginal bleeding, boggy fundus, hypotension
• Uterine fundal massage to maintain contraction
• If bleeding persists:
  • Oxytocin IV/IM
  • Methylergonovine (Methergine) 0.2 mg IM (if not hypertensive)
  • PGF₂α (Hemabate) 250 μg IM q15-20 min (up to 3 doses)
  • Misoprostol 200-1000 μg (oral/sublingual/vaginal/rectal)
• Inspect for cervical and vaginal lacerations after placental delivery
• Repair episiotomy/lacerations

True vs False Labour (Braxton Hicks)

Severe MR & Severe AR in Pregnancy - Management Guidelines

Overarching Principle

Pre-Pregnancy Counseling & Intervention

Indications to Intervene Before Attempting Pregnancy

"Surgical treatment is best undertaken before pregnancy. After successful mitral valve repair with significantly improved ventricular function, pregnancy may be undertaken successfully."

• Creasy & Resnik's Maternal-Fetal Medicine

Key Pre-Pregnancy Note on Prophylactic Valve Replacement

• Mechanical valve: maternal mortality ~1.4%, only 58% event-free pregnancies
• Bioprosthetic valve: maternal mortality ~1.5%, only 79% event-free pregnancies

WHO Risk Classification

Management During Pregnancy

General Principles (Both MR and AR)

1. Multidisciplinary team - cardiologist + obstetrician + anaesthesiologist at a referral/expert centre
2. Serial echocardiographic monitoring throughout pregnancy and postpartum
3. Avoid ACE inhibitors, ARBs, ARNIs (sacubitril/valsartan) - all teratogenic/fetotoxic
4. Avoid surgical valve replacement during pregnancy - high fetal loss risk with cardiopulmonary bypass
5. Monitor closely for arrhythmias (especially AF)

Medical Management of Severe MR in Pregnancy

1. Diuretics - furosemide (loop diuretic) - safe in pregnancy
2. Hydralazine - vasodilator (afterload reduction) - safe in pregnancy
3. Nitrates (isosorbide di/mononitrate) - safe in pregnancy
4. Digoxin - rate control + mild inotropy
5. Beta-blockers - for rate control if tachycardia

• ACE inhibitors (captopril, enalapril) - fetotoxic
• ARBs - fetotoxic
• Sacubitril/valsartan (ARNI) - contraindicated
• Spironolactone - avoid (anti-androgenic effects on fetus)

Medical Management of Severe AR in Pregnancy

• Rule out aneurysm/dissection at outset
• Serial echo for aortic root diameter every trimester
• If Marfan: beta-blockers throughout pregnancy regardless of symptoms
• Operative vaginal delivery (forceps/ventouse) to limit Valsalva stress if aortic root 40-45 mm

Mode of Delivery

• Epidural analgesia preferred (reduces cardiovascular stress of pain)
• Avoid fluid overload during labour
• Left lateral tilt to avoid aortocaval compression
• Assisted second stage (forceps/ventouse) to shorten pushing phase
• Have cardiac team available at delivery

Postpartum Management (Critical Period)

• SVR normalises rapidly after delivery
• But volume load (from uterine involution/autotransfusion of ~500 mL) persists
• This combination can precipitate acute pulmonary oedema

• Close monitoring for first 24-48 hours
• IV loop diuretics (furosemide) to reduce redistribution pulmonary oedema risk - especially for moderate-severe regurgitation
• Echocardiographic follow-up at 4-6 weeks postpartum
• Counsel regarding future pregnancies and planned valve surgery
• Can now restart ACE inhibitors/ARBs postpartum (caution if breastfeeding - enalapril considered safest)

Summary: Key Decision Points

Severe MR/AR - PRECONCEPTION
├── EF <40% + symptoms → Surgery BEFORE pregnancy
├── EF ≥45%, asymptomatic → Pregnancy possible with close monitoring (mWHO III)
└── EF <30% or NYHA III-IV → Advise against pregnancy (mWHO IV)

Severe MR/AR - DURING PREGNANCY (if presenting already pregnant)
├── Asymptomatic, preserved LV → Conservative: monitoring + salt restriction + diuretics PRN
├── Developing HF → Furosemide + Hydralazine + Nitrates
├── AF → Rate control + anticoagulation
├── Refractory HF, <22 weeks → Discuss termination
├── Refractory HF, >22 weeks → Maximise medical therapy; aim for 28-34 weeks then deliver
└── Valve surgery in pregnancy → Last resort; extremely high fetal loss risk