Los Angeles has pledged to phase in a ban by 2012.

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The rate of premature births was found to fall after each phase of the ban with the biggest impact seen after the second two bans with restaurants and bars introducing no smoking rules.

BBC: Smoking ban 'cuts premature births'

In the latest study researchers were able to look at the rate of premature births after each phase of a smoking ban came into force in Belgium.

BBC: Smoking ban 'cuts premature births'

Obviously, the ban would take some time to phase in, but the goal is to have no smoke and no smoking-related advertising in any public area in China by 2020.

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The study of 600, 000 births found three successive drops in babies born before 37 weeks - each occurring after a phase of a public smoking ban was introduced.

BBC: Smoking ban 'cuts premature births'