While most children can recover from bronchiolitis quickly, it can make the child more prone to other respiratory illnesses such as asthma later in life.

While most children can recover from bronchiolitis quickly, it can make the child more prone to other respiratory illnesses such as asthma later in life.

Babies born by elective caesareans are more likely to suffer a serious respiratory infection in their first year of life, according to Perth researchers.

The decade-long study into the incidence of Bronchiolitis found that babies born by elective caesarean were 11 per cent more likely to be hospitalised with the infection than babies delivered by other means.

Researchers at Perth's Telethon Institute for Child Health Research analysed birth data and hospital records for 212,068 babies over a 10-year period in WA for the study - the first of its kind to link elective caesareans to the infection.

Dr Hannah Moore led the study and said that while the increase was relatively modest, it highlighted the risk to a child's immune system when elective caesareans were the chosen birth method.

"We compared elective caesareans with other modes of delivery because with elective caesareans we could be confident that labour had not begun and therefore the baby would not have been exposed to [natural] chemicals that are released during the labour process," Dr Moore said.

"It is increasingly plausible that delivery without labour could impair a newborn's immune system and may also explain the known link between c-sections and an increased risk of asthma."

Dr Moore said that when the study commenced in 1996, elected caesareans accounted for 12 per cent of all WA births. This increased to 21 per cent in 2005, equating to an average of 16 per cent over the study period.

Bronchiolitis is generally caused by the common respiratory synctial virus and is one of the most common reasons for babies to be admitted to hospital.

She said that while most children recover from the infection quickly, it can make the child more prone to other respiratory illnesses such as asthma later in life.

Dr Moore said the research, published in the latest online edition of the international journal Archives of Disease in Childhood, pointed to the need for more research into the suspected role of various chemicals that are produced by mothers during labour in priming a newborn's immune system.

"Given that caesarean rates are rising in Australia, this potential impact on the immune system might be another factor that parents and doctors may consider if choosing a caesarean for other than medical reasons," she said.

"As it's the first time we have reported such an association, it's really important that the message get out there that women and their clinicians need to consider this when opting for a caesarean."