Smoking bans have been linked to a reduction in the number of babies born prematurely, according to new research.
Pregnant women have been subjected to less second-hand smoke since the law banning smoking in public places came into force.
Now researchers have shown the benefits of the ban, saying it reduced the risk of pre-term delivery.
Premature babies can suffer from significant health problems.
Researchers examined the effect recent smoking bans in Belgium had on the number of premature babies.
Smoking bans in the country were implemented in three phases - in public places and most workplaces in January 2006, in restaurants in January 2007, and in bars serving food in January 2010.
Data concerning 606,877 babies born in Flanders between 2002 to 2011 was analysed.
The researchers found reductions in the risk of pre-term birth, classed as such if babies were born before 37 weeks of pregnancy, after the introduction of each phase of the smoking ban, according to the paper published on bmj.com.
After the ban came into force on January 2007 the risk reduced by 3.13% and there was a further reduction of 2.65% after January 2010, researchers said.
“Our study shows a consistent pattern of reduction in the risk of pre-term delivery with successive population interventions to restrict smoking,” the authors wrote.
“It 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.”
Louise Silverton, director for midwifery at the Royal College of Midwives, said: “There is no doubt because it is supported by a large body of evidence, of the negative impact of smoking on the pregnant woman and her developing child and of the effects of second-hand smoke.
“This research is encouraging but we should also be aware that many pregnant women are still exposed to second-hand smoke in domestic situations.
“We would hope that smokers would be considerate and refrain from smoking when pregnant women are in their immediate vicinity.
“It is also important that when the baby is born that it spends as much time as possible - ideally all the time - in a smoke-free environment.”