OSLO, May 14 (Xinhua) -- New research conducted by Norwegian Institute of Public Health shows that high levels of diethylhexyl phthalate (DEHP) in pregnant women increase risk of their children developing Attention Deficit/Hyperactivity Disorder (ADHD), online newspaper Nettavisen reported Monday.

Phthalates are substances that are mainly used to soften plastic, and can be found in electrical products, pharmaceuticals, and medical equipment.

Out of many different phthalates, some are classified as harmful to reproduction and the environment, the report said.

This is the first time that such a study is being conducted in Norway. Researchers have only looked at children who have received an ADHD diagnosis, while previous studies conducted outside Norway have included children with ADHD symptoms and behavioral problems.

During the study, the researchers measured the amount of different phthalates in the urine of 850 pregnant women. In the group of pregnant women with the highest DEHP level, the risk that the baby had ADHD was almost three times as high as among those with the lowest DEHP level, the report said.

However, it could not be concluded that phthalates during pregnancy were the direct cause of ADHD, said Gro Dehli Villanger, one of the researchers.

"We need a lot more research to gain knowledge about mechanisms of action and causal factor between environmental toxins, including phthalate, and brain development in humans," Villanger said.

The use of DEHP, previously the most-used phthalate in Norway, has significantly decreased since 1997 and is forbidden in cosmetics, toys, and other products for toddlers both in Norway and the European Union (EU).

According to Norwegian health authorities, three to five percent of children under the age of 18 years have ADHD in Norway.