Mitral Stenosis in Pregnancy
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Direct answer
Mitral stenosis in pregnancy is narrowing of the mitral valve, most often rheumatic, and it becomes dangerous as pregnancy raises heart rate and blood volume while shortening diastolic filling. A valve area below 1.5 cm² indicates severe stenosis, and pulmonary oedema usually follows tachycardia, infection, anaemia, fluid loading or atrial fibrillation. Rate control with beta blockers, careful diuresis and a labour plan avoiding oxytocin bolus form the core of management.
What you must remember
- Severity: a mitral valve area below 1.5 cm² indicates severe stenosis, and raised pulmonary artery pressure or NYHA class III or IV symptoms signal high maternal risk.
- Haemodynamic stress: blood volume rises by about 40 to 50 per cent and heart rate increases, both of which shorten diastole and raise left atrial pressure.
- Pulmonary oedema triggers: tachycardia, atrial fibrillation, infection, anaemia, labour pain, fluid overload and oxytocin bolus.
- Heart rate control: beta blockers such as metoprolol are first line, and verapamil or diltiazem are used with caution, avoided in severe LV dysfunction.
- Intervention: percutaneous mitral balloon valvuloplasty is preferred for symptomatic severe stenosis not controlled medically, often in the second trimester.
- Labour: vaginal delivery is preferred, with epidural analgesia, slow oxytocin infusion and a shortened second stage using assisted delivery.
- Postpartum: the first 48 to 72 hours are high risk because of autotransfusion, so monitoring is needed.
A pathway from symptoms to a delivery plan
A 27-year-old with rheumatic mitral stenosis presents at 26 weeks with orthopnoea and a heart rate of 110. Her plan must reduce the rate, relieve congestion and decide whether valvuloplasty is needed, so each step addresses a specific stress point.
- Assess severity: echocardiography for valve area, mean gradient and pulmonary pressure, with NYHA class recorded.
- Control the rate: start a beta blocker, aiming for a slower rate that prolongs diastolic filling, with close monitoring.
- Relieve congestion: use oxygen, sitting position and loop diuretics, and avoid excess intravenous fluid.
- Intervene if needed: consider balloon valvuloplasty when symptoms persist despite medical therapy, usually in the second trimester.
- Treat atrial fibrillation: rate control and anticoagulation with heparin, since warfarin is avoided in early pregnancy and is used cautiously later.
- Plan labour: epidural analgesia, a slow oxytocin infusion, avoidance of prolonged pushing, and an experienced team ready for pulmonary oedema.
Each step is revisited at every antenatal visit, because heart rate, fluid status and rhythm can change within days.
Where the exam tries to catch you
Mitral stenosis questions reward the candidate who knows that tachycardia, not the valve alone, causes most decompensation in pregnancy.
- Trap: "Beta blockers are contraindicated in mitral stenosis." Correct: they are first line for rate control, as slowing the heart prolongs diastolic filling and reduces congestion.
- Trap: "Give an oxytocin bolus for a quick third stage." Correct: a bolus causes tachycardia and hypotension, so a slow infusion is used instead.
- Trap: "Treat epidural hypotension with a generous fluid bolus." Correct: fluid loading can precipitate pulmonary oedema, so a vasopressor such as phenylephrine is preferred with cautious fluids.
Frequently asked questions
What mitral valve area indicates severe mitral stenosis in pregnancy?
A mitral valve area below 1.5 cm² indicates severe mitral stenosis, and this threshold matters when planning pregnancy counselling and labour. Pulmonary artery pressure and NYHA class further refine the maternal risk.
Why is tachycardia dangerous in mitral stenosis during pregnancy?
Tachycardia shortens diastolic filling time across a narrowed mitral valve, so left atrial pressure rises and pulmonary oedema can follow. This is why rate control with beta blockers is central to managing mitral stenosis in pregnancy.
Is vaginal delivery safe in mitral stenosis?
Vaginal delivery is generally preferred in mitral stenosis, with epidural analgesia, slow oxytocin and a shortened second stage. Caesarean is performed for obstetric reasons, not automatically, since surgery carries its own haemodynamic risks.
When is balloon valvuloplasty considered in pregnant women with mitral stenosis?
Percutaneous mitral balloon valvuloplasty is considered for symptomatic severe mitral stenosis that does not respond to medical therapy, often in the second trimester. The procedure is performed with fluoroscopy minimised and fetal shielding used.