(Reuters Health) - One year after a nationwide ban on smoking in public took effect in Spain, women had significantly fewer premature or underweight infants, a recent study suggests.
Researchers examined data on more than 5 million babies born in Spain from 2000 to 2013. The study included infants born before any restrictions on public tobacco use, after a 2006 ban covering many workplaces with exceptions in the hospitality industry, and after a 2011 law curbing tobacco in nearly all public places.
The rate of babies born small for their gestational age declined after the partial smoking ban took effect in 2006, researchers report in Pediatrics. With the comprehensive ban in 2011, rates of preterm and low-birthweight babies also dropped.
"Second hand smoke exposure during pregnancy is associated with health complications affecting perinatal and neonatal health," said senior study author Dr. Inaki Galan of the Autonomous University of Madrid.
"The implementation of two Spanish smoking bans (partial and comprehensive) was associated with a risk reduction regarding preterm births and low birth weight infants," Galan said by email.
Pregnancy normally lasts about 40 weeks, and babies born after 37 weeks are considered full term. Babies who arrive earlier often have difficulty breathing and digesting food in the weeks immediately after birth. Preemies can also encounter longer-term challenges such as impaired vision, hearing and cognitive skills as well as social and behavioral problems.
Overall, the researchers found that during the study period 7.9 percent of infants were premature, 9.2 percent were small for their gestational age and 7.8 percent had low birth weight.
The comprehensive smoking ban was associated with an immediate 4.5 percent reduction in the preterm birth rate that was sustained a year after the law took effect. The birth rate of underweight babies fell 2.3 percent immediately and fell a bit more one year after implementation.
With the partial ban, the study found an immediate 4.9 percent reduction in the birth rate of babies that were small for their gestational age.
The study wasn't a controlled experiment designed to prove how full or partial smoking bans might directly influence how soon babies arrive or how big they are when they're born.
Other limitations of the study include the lack of data on the mothers' smoking habits or whether they worked outside the home, both of which could influence how much the bans contributed to changes in tobacco exposure for babies during pregnancy.
Still it's possible that the bans work two ways to help limit developing babies' exposure to tobacco, said Dr. Karen Wilson of the Icahn School of Medicine at Mount Sinai and Kravis Children's Hospital in New York.
"Not only do smoking bans reduce the number of places where a mother might be exposed, it creates an incentive for people to quit, so it's more likely that a mom or her partner will quit entirely," Wilson, who co-wrote an accompanying editorial, said by email.