It can difficult to monitor a baby's heart

Previous techniques which have been used to monitor a baby's heartbeat in the womb have not been completely reliable.

In part this is because it has proved difficult to screen out background interference, such as the sound of the mother's heart.

By getting more information on the hearts of unborn babies, it may be possible to detect those at high risk Dr Helena Gardiner

The new device solves this problem by employing sophisticated filtering and amplification systems.

It has been tested by a team from Imperial College London, who hope it will prove particularly useful for monitoring pregnancies where there is a risk of pre-eclampsia, or a family history of abnormal heart rhythms.

Researcher Dr Helena Gardiner said: "Cardiac arrhythmia is believed to be a factor in cot death.

"By getting more information on the hearts of unborn babies, it may be possible to detect those at high risk and prevent the devastating effects of some arrhythmias on the foetus and newborn baby."

Widely tested

The 20-minute test, tested on more than 600 pregnant women at hospitals in London, involves placing electrodes on the mother's stomach.

The signal from these electrodes is then relayed back to a computer which can pick out the baby's heart signal from background interference.

Dr Myles Taylor, who also worked on the study, said: "Although it has been possible to record the fECG (full foetal ECG) from the baby in the womb since the 1960s, the technique has not been totally reliable, as it is difficult to separate the heart rate from background interference.

"This new technique will allow us to accurately record and analyse the foetal ECG, not just in single pregnancies, but also in multiple pregnancies which we believe is a world first."

The technology has been developed by a company called QinetiQ.

The research is published in the British Journal of Obstetrics and Gynaecology.