An e-cigarette researcher is urging pregnant women to avoid e-cigarettes and vaping because of the lack of evidence suggesting it is safe to do so.

Pregnant women are being urged to avoid e-cigarettes and vapes due to a lack of evidence about their safety.

E-cigarette researcher Associate Professor Alexander Larcombe says many people believe vaping or smoking e-cigarettes is safer than tobacco smoking during pregnancy.

"It is completely unfounded and almost certainly not true," Dr Larcombe said.

"Women and babies are still potentially getting exposed to nicotine and other potentially harmful chemicals.

"My concern is we just don't know what the effects are on the unborn baby."

People aged between 18-39 are Australia's biggest e-cigarette users.

In recent research, Dr Larcombe found six out of 10 "nicotine-free" labelled e-cigarettes contained nicotine.

A toxic chemical, typically found in pesticides and disinfectants, was also present.

He said literature suggests nicotine has the greatest impacts on an unborn baby's health.

"It impacts brain development, so it affects the behaviour, memory and learning of the child," he said.

"It also affects lung growth and development and affects the range of other organs in a negative way as well."

Dr Larcombe said further research was needed.