Ireland’s implementation of a workplace smoking ban in 2004 appears tied to a decline in maternal smoking rates as well as lower risk for preterm births, study findings hint.

Compared with the year prior to the smoking ban, 12 percent fewer women reported smoking during pregnancy in the year after the ban, Dr. Zubair Kabir, of the Tobacco Free Research Institute in Dublin, Ireland, and colleagues report.

Their study, in BJOG: An International Journal of Obstetrics and Gynaecology, also revealed “a welcome sign,” Kabir’s team notes. They observed 25 percent lower risk for preterm births in the year after the smoking ban compared with the year prior to the ban.

Kabir and colleagues analyzed records at Coombe Women and Infants University Hospital to assess whether Ireland’s workplace smoking ban altered smoking during pregnancy, a known risk factor for preterm birth and having a low birth weight infant.

Their comparison included 7,593 births in 2003 and 7,648 births in 2005, and allowed for other maternal factors tied to birth risks such as the mother’s age, number of previous births, alcohol intake, blood pressure, and complications during pregnancy.

Overall, babies with the highest birth weights on average were born to former smokers. By contrast, babies with the lowest birth weights had mothers who smoked during pregnancy.

However, in addition to the noted declines in maternal smoking and preterm birth risk, the investigators also identified 43 percent greater risk for low birth weight in the year after the smoking ban compared with the year prior to the ban.

This finding “is intriguing and needs further exploration,” Kabir and colleagues say, particularly in light of evidence that exposures to secondhand smoke during pregnancy may play a role in having babies with low birth weight.

They also call for further exploration of their observed increase in Caesarean delivery rates - from 15.4 in 2003 to 19.5 percent in 2005.

SOURCE: BJOG, An International Journal of Obstetrics and Gynaecology, December 2009