The problem with pregnancy and PH
So why is it that women with PH are advised they shouldn’t have children? Your medical team just wants the best for you. The studies that are available all suggest that pregnancy in a woman with PH is incredibly risky and can lead to loss of life.
How does pregnancy affect the health of a woman with PH?
When a woman is pregnant there are lots of changes that happen within their body. There are three main changes which are important in PH: an increase in what is called cardiac output, a decrease in peripheral vascular resistance, and an increase in the likelihood of thrombosis. We address each of these below.
This is the amount of blood that the heart pumps through the body. As the pregnancy develops, the heart has to pump more blood around the system which in turn means that the heart has to work harder than it would do normally. The cardiac output increases steadily from when pregnancy begins and reaches its peak at around 24-26 weeks of pregnancy.
In pulmonary hypertension, the heart is already working harder than normal which is why getting pregnant can have such a negative impact on a woman’s health. In some women, the heart simply cannot meet the new demands placed on it by the pregnancy and there can be a significant increase in breathlessness and syncope (fainting).
Peripheral vascular resistance
This affects how easy it is for the blood to flow through the blood vessels. In pregnancy, the resistance steadily decreases which makes it easier for the blood to travel around the body. It also makes it easier for the blood to flow through the lungs. Part of the disease process in PH increases vascular resistance in the lungs so in women with PH, the changes in the vascular resistance during pregnancy can actually improve symptoms. This can give the impression that all is well, but things change very quickly once the baby is born.
Immediately after having a baby, there are several significant changes within the cardiovascular system (heart and blood vessels) which bring a high risk to the mother’s health. The peripheral resistance rapidly returns to what it was before the pregnancy. In a woman with PH, there is a bigger change in the blood flow through the lungs than in a woman without PH. As the blood flow around the lungs suddenly comes up against more resistance, PH symptoms can worsen. There is also a massive change in the amount of fluid circulating through the heart and main vessels. The combination of extra fluid circulating and a sudden increase in resistance to the blood flowing around the lungs, puts a huge amount of pressure on the heart. This is why the period after having a baby is a very risky time.
This is the formation of a blood clot within a blood vessel which prevents blood flowing through that vessel. During pregnancy and for six weeks afterwards, the blood becomes ‘hypercoagulable’. This means it clots more easily and is why any pregnant woman, or a woman who has given birth up to six weeks previously, is at a higher risk of a blood clot in her legs or her lungs than a woman who isn’t pregnant. For a woman with PH, even if the PH is not linked to blood clots of the lungs, the impact of having a blood clot can be very damaging to her health.
Because of these changes, pregnancy, childbirth and the immediate post-natal period all carry a high risk to the mother’s health. And because of this, the medical advice for any woman with pulmonary hypertension is to avoid getting pregnant.
How does PH affect the health of the unborn child?
If a woman with PH becomes pregnant, assuming their heart and lungs work well enough, there is no indication that the disease itself has any harmful effects on the developing foetus.
However, the medication that the woman would need to take to keep the heart and lungs working well, may have effects on the baby.
Information about the safety of drugs during pregnancy is collected differently to information about the general safety of drugs. It is not ethical to organise a study for a new drug using pregnant women because of the possible risk to the foetus. Information is therefore only available from animal studies and from anecdotal evidence (other women’s stories).
Because PH is a rare condition and because successful pregnancies are even rarer, there is not a lot of anecdotal evidence. So, most of the information we have is from animal studies.
Due to the results of animal studies, some of the medications used in PH are ‘contra-indicated’ in pregnancy – in other words, they shouldn’t be used at all, as they are known to cause damage to the unborn child.
PH-specific medications that are contra-indicated are Ambrisentan, Bosentan and Macitentan. Non-PH specific, but frequently used medication that is contra-indicated, is warfarin.
Other medications used in PH are not contra-indicated but, as there is very little information about their safety, the advice is usually to use with caution.