Low birthweight and preterm birth rates 1 year before and after the Irish workplace smoking ban

Abstract

Objective: It is well-established that maternal smoking has adverse birth outcomes (low birthweight, LBW, and preterm births). The comprehensive Irish workplace smoking ban was successfully introduced in March 2004. We examined LBW and preterm birth rates 1 year before and after the workplace smoking ban in Dublin.

Design: A cross-sectional observational study analysing routinely collected data using the Euroking K2 maternity system.

Setting: Coombe University Maternal Hospital.

Population: Only singleton live births were included for analyses (7593 and 7648, in 2003 and 2005, respectively).

Methods: Detailed gestational and clinical characteristics were collected and analysed using multivariable logistic regression analyses and subgroup analyses.

Main outcome measures: Maternal smoking rates, mean birthweights, and adjusted odds ratios (ORs) of LBW and preterm births in 2005 versus 2003.

Results: There was a 25% decreased risk of preterm births (OR, 0.75; 95% CI, 0.59-0.96), a 43% increased risk of LBW (OR, 1.43; 95% CI, 1.10-1.85), and a 12% fall in maternal smoking rates (from 23.4 to 20.6%) in 2005 relative to 2003. Such patterns were significantly maintained when specific subgroups were also analysed. Mean birthweights decreased in 2005, but were not significant (P=0.99). There was a marginal increase in smoking cessation before pregnancy in 2005 (P=0.047).

Conclusions: Significant declines in preterm births and in maternal smoking rates after the smoking ban are welcome signs. However, the increased LBW birth risks might reflect a secular trend, as observed in many industrialised nations, and merits further investigations.