A third of pregnant women in Japan do not regularly fasten their car seat belts, according to an Internet survey released Tuesday.

The poll was conducted by the Web site Baby Come Online -- www.babycome.ne.jp/ -- which was created by and for pregnant women. It quizzed 310 women who were either pregnant or mothers of young children. Their responses were based on their car habits during pregnancy.

Thirty-three percent said they fastened their seat belts occasionally or never. The other 66 percent said they always made sure to buckle up.

Among the former group, 70 percent said they believe that pregnant women do not need to buckle up, while 19 percent said they did not know how pregnant women should fasten their seat belts.

Unlike many other developed countries, Japan does not legally require pregnant motorists or passengers to use seat belts.

Officials at Baby Come Online said that in many cases in Japan, doctors, nurses and police officers tell pregnant women they either do not need to buckle up or that seat belts can damage the uterus.

Some researchers, however, say that advice does not appear to be supported by scientific literature.

"So far, there have been no reports of harm caused to the bodies of pregnant women when they fasten their seat belts," said Hiroshi Murao of Okinawa Chubu Hospital, who has researched pregnancy-related injuries.

"If the shoulder belts lie across the chest and fasten at the lap, and the lap belts go under the uterus, then there should be no problem."