Smoking bans have led to a reduction in premature births, a new study has found.

According to Belgian scientists, it is already well established that smoking during pregnancy can impair the growth of a foetus and lead to a premature (preterm) birth. Exposure to passive smoking can also have a detrimental effect.

However, little research has been carried out to assess the possible impact of smoking bans on premature births, so the scientists decided to investigate this further.

Smoking bans were introduce in Belgium in three phases:
-January 2006 - public places and most workplaces
-January 2007 - restaurants
-January 2010 - bars serving food.

The scientists studied over 600,000 live births that took place in Flanders between 2002 and 2011. A birth was considered premature if it took place before 37 weeks gestation.

The study found reductions in the risk of premature births after the introduction of each smoking ban phase. No such trend was found at any other time during the study period.

After the 2007 ban, the risk of premature births fell by 3.13%. After the 2010 ban, it fell by a further 2.65%.

The results stood even when other factors were taken into account, such as the mother's socioeconomic status and levels of air pollution at the time.

The scientists from Hasselt University said that their study revealed ‘a consistent pattern of reduction in the risk of preterm delivery' following the smoking bans.

"This supports the notion that smoking bans have public health benefits even from early life. More and more countries in Europe are adopting stricter legislation on smoking in public places. These results underscore the public health benefit of smoking ban policies," they said.

Details of these findings are published in the British Medical Journal.