Pregnancy With Valvular and Congenital Heart Disease
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Direct answer
Heart disease in pregnancy is assessed with the modified WHO maternal cardiovascular risk classification, which sorts women into classes I to IV. Pregnancy raises heart rate, stroke volume and plasma volume, which can decompensate a stenotic mitral valve, so beta blockers and careful diuresis are used. Class IV conditions, such as pulmonary arterial hypertension, carry extreme risk and usually mean counselling against pregnancy.
What you must remember
- mWHO class I: no increased maternal risk, so pregnancy can proceed with routine obstetric care.
- mWHO class IV: pulmonary arterial hypertension and severe ventricular dysfunction carry extreme risk, and pregnancy is generally contraindicated.
- Mitral stenosis: the most poorly tolerated valve lesion, because tachycardia shortens diastolic filling and raises left atrial pressure.
- Beta blockers: slow the heart rate in mitral stenosis, which improves diastolic filling time.
- Balloon valvotomy: percutaneous balloon mitral valvotomy can be done in pregnancy for symptomatic severe stenosis, often in the second trimester.
- Mechanical valves: these need anticoagulation throughout pregnancy, and warfarin embryopathy is most concerning at about 6 to 12 weeks, so heparin is often substituted then, though some guidelines allow low-dose warfarin.
- Heparin switch: low-molecular-weight heparin replaces warfarin early in pregnancy, and unfractionated heparin is used near term.
- Teratogens: ACE inhibitors, angiotensin receptor blockers and statins are avoided because of fetal harm.
A pathway from preconception to delivery
Outcomes depend on planning before conception, because the most dangerous decisions are made before the first missed period. The steps run from risk classification to anticoagulation and delivery.
- Classify before conception: Assign the mWHO class and counsel against pregnancy in class IV, because the risk of death or severe decompensation is too high.
- Control the lesion: Symptomatic mitral stenosis is managed with heart rate control and careful diuresis, and balloon valvotomy is considered if medication fails.
- Plan anticoagulation: Mechanical valves need anticoagulation, and the choice between warfarin and heparin is made with the team, because warfarin embryopathy is most concerning from about 6 to 12 weeks.
- Use the safest drugs: ACE inhibitors, angiotensin receptor blockers and statins are stopped, and labetalol or nifedipine are preferred for hypertension in pregnancy.
- Monitor serially: Echocardiography is repeated through pregnancy, and symptoms and echo findings guide escalation of care.
- Plan delivery and the postpartum period: A multidisciplinary plan covers the anticoagulation switch and haemodynamic monitoring, because fluid shifts in the first days after delivery can precipitate pulmonary oedema.
Where pregnancy plans go wrong
Errors usually come from changing medicines without considering both mother and fetus.
- Trap: switching a mechanical valve patient to aspirin during pregnancy Correct: aspirin does not provide adequate valve protection, so anticoagulation with heparin or warfarin continues.
- Trap: continuing warfarin unchanged through the first trimester Correct: warfarin embryopathy is most concerning from about 6 to 12 weeks, so a safer regimen is planned.
- Trap: starting an ACE inhibitor for left ventricular dysfunction in pregnancy Correct: ACE inhibitors and angiotensin receptor blockers cause fetal renal toxicity and are avoided.
Frequently asked questions
What is class IV in the modified WHO maternal risk classification?
Class IV is an extremely high-risk category in which pregnancy is contraindicated, with pulmonary arterial hypertension as the classic example. Women in this class are counselled about contraception and the risk of maternal death.
Why is mitral stenosis poorly tolerated in pregnancy?
Mitral stenosis is poorly tolerated because tachycardia and higher blood volume shorten diastolic filling and raise left atrial pressure. Pulmonary oedema can follow, which is why heart rate control is central to management of mitral stenosis in pregnancy.
Which anticoagulant is used for mechanical valves in the first trimester?
Low-molecular-weight heparin is commonly used in place of warfarin in the first trimester for mechanical valves, because warfarin causes embryopathy. Unfractionated heparin is used near term, and the switch is planned with the cardiology and obstetric teams.
Which drugs must be avoided in pregnancy with heart disease?
ACE inhibitors and angiotensin receptor blockers are avoided because they harm the fetal kidneys, and statins are stopped in pregnancy. Warfarin is avoided in the first trimester, and every drug choice is reviewed with the obstetric team.