Pregnancy in women with hypertrophic cardiomyopathy (HCM)

With a thickened heart muscle, the thickening can vary in distribution and severity.

If you have heart muscle thickening, the heart muscle is stiffer than normal although the contraction of the muscle is good. If the heart muscle is thick, it can obstruct the blood flow leaving the heart and this can lead to symptoms such as chest pain, breathlessness and blackouts. You may also have problems with the electrical conduction system and get heart rhythm problems (arrhythmias).

If you already have symptoms of breathlessness and chest pain, they are likely to get worse when you are pregnant, mainly because the demand and workload on the heart is increasing. If you have arrhythmias they may worsen. But most of these problems and symptoms can be controlled with medicines. I use betablockers a lot and they are safe in pregnancy. Symptoms of breathlessness tend to respond to small doses of diuretic.

If you do not suffer with arrhythmias but have an ICD or a pacemaker we will use aspirin as a mild blood thinner during pregnancy to prevent clots forming on the leads of the devices. If, however, you have arrhythmias we use a more potent blood thinner in the form of low molecular weight heparin injections as pregnancy encourages blood clots. Low molecular weight heparin is safe and it doesn’t affect the baby but you have to inject yourself twice a day for the whole nine months.

What to expect in pregnancy

Usually your antenatal care is normal and you will have obstetric reviews like any other mother. But you will have more frequent cardiology reviews – about every four to eight weeks. A lot depends on whether the heart muscle thickness is severe or mild; the more severe the problem the more frequently you will have to be seen.

We sometimes do echos but not routinely in HCM but would perform one if somebody has significant symptoms or is not responding to treatment. If you start to get more palpitations, we might also check the ICD, just to make sure it is not just the normal fast heart beat of pregnancy and there’s no rhythm issues. The majority of women with HCM will have a normal vaginal delivery at full term. There is still a tendency for many cardiologists to think that Caesarean section is safer for women with a heart problem, but it’s not. Caesarean section is associated with more bleeding, increased infection, epidurals and general anaesthesia and you have to balance those risks.

If you have a pacemaker or ICD and are to have your baby in London, we recommend a planned induction for a vaginal delivery and have technicians available who can programme the device if needed. This is because during a C-section diathermy, a surgical technique using heat, is used and this can interfere with devices.


There is a low risk of complications if you have:

  • mild heart muscle thickening
  • no or little obstruction to blood outflow from your heart
  • only a slight leak from your mitral valve
  • no arrhythmia or well controlled arrhythmias
  • do well on an exercise test

If you can manage more than six minutes on a treadmill or you achieve more than 60 per cent predicted on a VO2 cardio-pulmonary exercise test, you are likely to cope with being pregnant.
If you have severe thickening of the heart muscle, severe obstruction to the blood flow out of the heart, your mitral valve is severely leaky, your arrhythmias are not properly controlled and your exercise test is not good, you will find pregnancy very difficult and there’s a high chance of complications.

In our experience at the Heart Hospital (reasonable numbers for a single centre) we found that symptoms of breathlessness and arrhythmias tend to worsen if present beforehand and some patients developed heart failure (fluid congestion on the chest) if experienced before. Around 60 per cent of women in our service delivered vaginally, mainly because with a first-time baby, trying to induce labour a bit early (38 weeks) has a 50 per cent chance of achieving normal delivery and therefore 50 per cent end up with a Caesarian section. Elective Caesarean sections were mainly for obstetric reasons.

Previous data from St George’s Hospital showed similar results. Patients became more breathless, they sometimes got palpitations and chest pain, and symptoms did tend to worsen, but less than 10 per cent of women had serious symptoms. There were no deaths and there have been none in our care at the Heart Hospital so far.