One baby in 100 is born with heart or circulation problems. With improvements in ultrasound scan techniques, most can now be detected while the baby is still in the womb
Causes of heart problems
It’s thought that most heart problems in babies are due to faulty genes. From conception, when sperm and egg combine, a complex construction process occurs to create a human embryo. We all carry a small number of faulty genes and if there’s a fault in the gene signalling, a structural heart problem may appear.
In small communities, where relatives are more likely to marry, there is less variation in the genes and it is more likely that both parents will carry the same rare genetic faults. This situation is known as a small gene pool, and it’s dangerous because genetic conditions such as heart abnormalities are more likely to occur. In larger communities, where there’s more mixing of different genes, genetic problems are less common.
A proportion of babies with heart malformations have problems with the chromosomes, which can be detected by tests during pregnancy, providing an early clue that the child may be at particular risk. For example, many pregnant women are screened for Down’s syndrome (where there are three rather than two copies of chromosome number 21), in which up to 40 per cent of babies are born with a heart problem.
There are other causes of congenital heart disease too. For example, mothers with diabetes have a two per cent chance of having a baby with a heart problem.
However, most of the babies born with heart problems don’t come from high-risk groups. The reason is simply that this is a comparatively rare, almost unpredictable condition – and there are only small numbers of high-risk people in the population.
Diagnosing heart problems
The majority of heart problems in babies are detected at a routine ultrasound scan, usually at 18 to 20 weeks, although some aren’t discovered until after the birth. If you have worries, talk to your GP or obstetrician. If they suspect problems, they may refer you to a specialist unit for further tests.
At about 19 weeks gestation, a baby’s heart is less than 1cm across and weighs only 1g or so (compared with 500g for an average adult heart). It also beats more than twice as fast as an adult’s.
The circulation of a foetus is different from that of a newborn baby, being connected to a placenta and having three extra channels that must close or reverse at birth.
Good-quality ultrasound equipment is essential to look at the tiny, fast-moving cardiac structures. Even so, ultrasound images appear grainy – it requires practice and an experienced eye to identify problems.
Advances such as the colour flow doppler detect the movement of red blood cells, highlighting areas of abnormal blood flow that may indicate circulation problems. These may have been missed by a conventional scan.