CARS are as dangerous for pregnant women as alcohol and cigarettes, yet few mums-to-be are warned of travel risks, a leading injury researcher says.

New research by University of Otago found 21 unborn babies and newborns died in car smashes on New Zealand roads between 1997 and 2008.

A further 20 died following a fall, an assault or in other unexplained circumstances.

Lead researcher Professor Hank Weiss said the statistic was on par with the number of children hit and killed in driveways, yet few people are aware because the problem is "hidden" by data collection methods.

"The risks, as we've shown, are significant," Prof Weiss, director of the university's Injury Prevention Research Unit, told NZ Newswire.

"It's on par with the other risks of pregnancy that doctors advise about, like drinking and smoking, and yet it's not something that women are warned of.

"But they deserve to know."

While the findings, published in the journal Australian Epidemiologist, give pregnant women another thing to worry about, fortunately the risks could be easily managed.

He urged mums-to-be to consider driving less, always wear seatbelts, and avoid driving in the rain or at night, whether as a passenger or a driver.

The study, the first of its kind in New Zealand, calculated deaths of foetuses and newborns less than a month old.

It found Maori women were over represented in the statistics, probably because they were having children younger, when they were more likely to be involved in a car crash.

Prof Weiss said it was likely the statistics had been creeping up since the 1960s as women took to the wheel more and travelled longer distances.

In a grim reminder, he said the foetal death figures were "just the tip of the iceberg".

Many more babies were being born with neurological or physical injuries, often prematurely, as the result of car accidents. However, the defects are not recorded as injuries.

Originally published as Pregnant mums warned of driving risk