A small number of women, such as those with heart diseases, will need extra monitoring in the course of their pregnancy.

Worldwide, up to 1 per cent of pregnant women may have some form of heart disease. This is either pre-existing or developed in the course of the pregnancy.

Some women are born with congenital heart defects. About 0.8 per cent of all live births have this condition, said senior consultant cardiologist Tan Ju Le from the National Heart Centre (NHC).

It can range from a hole in the heart to defective ventricles and can lead to more serious problems such as Eisenmenger’s syndrome where heart defects give rise to higher blood pressure in the lungs.

This higher pressure damages fine blood vessels in the lungs, reducing the amount of oxygen that enters the blood to be transported to other organs.

It results in a “blue mother” with low oxygen levels in the blood for the baby and greatly reduces the chance of a live birth if a woman has this syndrome, said NHC’s Dr Tan.

The risk of the mother dying, especially in the later stages of pregnancy, is about 30 to 40 per cent, she added.

Pre-existing heart conditions can also arise from diseases suffered when the women were younger, such as rheumatic fever, which damages the heart.

However, such cases are now less common among locals and are mainly found in immigrants, said Dr Tan Lay Kok, a senior consultant at the obstetrics and gynaecology department at Singapore General Hospital (SGH).

There are also some mothers who have no history of heart disease but develop a heart problem called peripartum cardiomyopathy in the course of pregnancy. This condition, which causes the heart muscles to weaken, tends to strike in the last month of pregnancy or in the first five months after delivery. Heart failure can occur.

While the exact cause is still being researched, it only affects a small number of pregnant women. Other cardiovascular conditions, such as hypertension and diabetes, may hit pregnant mothers too.

Both can occur in women not known to previously have the disease and can adversely affect the baby, causing premature delivery or foetal death.

Hypertension, in particular, can indicate a more serious problem such as preeclampsia, where a spike in the blood pressure and in the protein level in the blood threaten the placenta and the baby’s life.

The mother may have a seizure. Preeclampsia, which can occur as early as in the 26th week of pregnancy, largely affects very young or older mothers, first-time mothers, women carrying multiple babies and those with underlying chronic problems like high blood pressure and obesity, said SGH’s Dr Tan.

Premature delivery is sometimes the only way to save both the mother and baby’s lives – but a premature baby faces many challenges, he said.

Women who have a pre-existing heart problem and are considering having a baby should discuss this with their doctors.

This is because their condition can get worse from the increased demands on their heart during pregnancy, said doctors. Patients with high-risk heart defects may be advised to undergo surgery before considering pregnancy or to put off the decision to bear children, said SGH’s Dr Tan.

For those whose condition can be controlled, treatment methods would vary depending on the condition faced by the mother.

Treatment methods typically involve lifestyle changes or drugs. However, drugs are often not an option as some medication can affect the baby, said NHC’s Dr Tan.

A British report in 2007 – The Confidential Enquiry Into Maternal And Child Health – showed that cardiac problems were the leading indirect cause of death in pregnant women living in Britain between 2002 and 2005, accounting for 30 per cent of the indirect maternal deaths there.

Doctors whom Mind Your Body spoke to expect the number of mothers with heart disease to rise.

NHC’s Dr Tan said one reason for this is that more children with congenital heart diseases now survive to adulthood. Another reason is that more women are postponing childbirth and older women tend to have more problems such as high blood pressure and diabetes, she added.

Up to 1% of pregnant women may have some form of heart disease.

This article was first published in Mind your body, The Straits Times.