A U.K. health watchdog released new guidance Thursday proposing that all pregnant women be subject to breath tests to check whether they have been smoking.

The National Institute for Health and Clinical Excellence (NICE) proposed that midwives administer breath tests to expectant mothers during their first prenatal appointment to measure the level of carbon dioxide in the body. The results are intended to make pregnant women realize the harm smoking can do to their child.

NICE says women who fail the test would be offered services to help them quit smoking.

"This isn't to penalize them but will be a useful way to show women that both smoking and passive smoking can lead to having high levels of carbon monoxide in their systems," Mike Kelly, of NICE, said.

Critics of the proposal, however, warn that the tests could embarrass expectant mothers rather than promote healthy behavior.

Sue Macdonald, of the Royal College of Midwives, said that health workers should focus on being supportive "rather than making women feel guilty."