Women who smoke during pregnancy and after giving birth may risk damaging the hearing of their children, a study suggests.

Nicotine exposure before birth and during breastfeeding can cause a key brain region that processes sound to develop abnormally, results from a mouse study show.

The research is the first to demonstrate that the auditory brain stem is vulnerable to nicotine.

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Children with impaired function in this part of the brain are likely to have learning difficulties and problems with language development.

The German scientists added nicotine to the drinking water of pregnant mice at levels equivalent to those taken up by heavy smokers.

After the offspring were born, the firing and signalling function of neurons in their brains was tested.

Compared with unexposed offspring, neurons sensitive to input from the inner ear were less good at transmitting signals to other brain cells.

The signals they did transmit were also less precise, so that the coding of sound patterns was disrupted, the findings published in The Journal of Physiology showed.

Lead researcher Professor Ursula Koch, from the Free University of Berlin said: "We do not know how many other parts of the auditory system are affected by nicotine exposure. More research is needed about the cumulative effect of nicotine exposure and the molecular mechanisms of how nicotine influences the development of neurons in the auditory brain stem.

"If mothers smoke during pregnancy and their children show learning difficulties at school, they should be tested for auditory processing deficits.'

Nicotine exposure during pregnancy was already known to harm foetal brain development.

Mothers who smoke or use e-cigarettes or nicotine replacement therapy have an increased risk of premature delivery or giving birth to a lightweight child. They are also more likely to experience sudden infant death.