It is a gadget like a Walkman and it plays knocking and whooshing sounds through your expanding abdomen which are said to stimulate your baby's mental development.
The sounds mimic the mother's heart beat and it is the subtle differences between these and the real thing that are believed to arouse the baby's curiosity and keep its brain cells developing.
But the BabyPlus, which is made in the US, does not come cheap. At pounds 202.50 it would pay for a lot of nappies and reflects a national obsession with the health quick fix. Medical experts remain sceptical.
Sue Taylor, head of BabyPlus in the UK, said 6,000 had been sold over the past three years. "It kick starts the thinking process. I used it with my fourth child and the improvement in his attention span compared with the others is the most exciting thing."
Developed by US psychologist, Brent Logan, the theory is that by stimulating the baby's brain, the device causes more nerve connections to be laid down so that the brain cells do not die off at birth. Around 40 per cent of brain cells are said to perish because they fail to connect to other cells.
Babies born after use of the device are said to be more supple, more alert, with better muscle and head control. The gadget is especially popular in the Far East and a large research study is underway in India and Russia.
Ms Taylor said: "I wish it was much cheaper but that is just the way it works. It was expensive to develop and there are just not enough mothers wearing it. There are also royalties to be paid to Dr Logan."
Dr Sarah Brewer, a GP who is writing a book on pre-natal stimulation, said most people were sceptical of its benefits until they saw the results. "My son's eyes were open when he was born and he had excellent head control. A lot of this is anecdotal and we are just at the stage where the evidence is coming in but there is enough for me to feel there is a benefit there. It is about trying to give your baby the best possible start in life."
Obstetricians say there is clear evidence that babies respond to stimulation in the womb and that, once born, a baby that is left unstimulated will not develop. There is no evidence, however, that playing sounds to the baby before birth in the womb is beneficial.
Dr John Friend, spokesman for the Royal College of Obstetricians and Gynaecologists said: "Diet and environment - whether the mother drinks or smokes - are likely to be more important for the baby's development than this device. It is probably not worth the money."
Parents' anxiety about their offspring make them ready consumers of new ideas. A missionary in China trying to earn his fare home claimed to have invented a medicine that would produce a baby boy. The potion came with a money-back guarantee if it failed. The canny inventor only had to return half the money - and got rich.