Washington, July 15 - An Indian American researcher has identified a potential bio-mechanism that could explain why oral contraceptives seem to fail in preventing pregnancy among obese women.

Although oral contraceptives appear to reach the required blood level concentrations to prevent pregnancy in such women, they may take twice as long to do so, leaving a 'window of opportunity' for pregnancy every month.

The findings are of particular importance, researchers noted, because about 30 percent of all US adults are obese and the birth control pill is one of the most popular forms of contraception in the nation.

'We don't have enough data yet to recommend that physicians change their clinical practice for use of oral contraceptives with patients who are very overweight,' said Ganesh Cherala, assistant professor in the College of Pharmacy at Oregon State University (OSU).

Cherala, who did his Bachelor of Pharmacy from Osmania University, Hyderabad, India, in 1999, said: 'Until more studies are done, women may wish to consult their physicians about this issue and consider a backup method of contraception.