Smoking Ban Law in Chile: Impact in Newborns' Birth Weight by Women's Age Groups and by City Population Density

Abstract

Objectives: We examined the short-term impact of the Smoking Ban Law (SBL) enacted in Chile in 2013 on low birth weight (LBW) rates in cities and its differential effects by different maternal age groups and city density. Methods: We included 885,880 live births from 21 Chilean cities of ≥100,000 inhabitants. We examined the smoking and LBW prevalence distribution before and after the SBL. Through Poisson mixed effect models, we determined whether a meaningful change in LBW rate occurred after SBL implementation in the whole sample and stratified by city population density and maternal age group. Results: LBW prevalence remained stable before and after the SBL implementation (6.1% and 6.3%, respectively), while women's smoking prevalence had a relative reduction of 25.9% (p < 0.00001). No significant changes in LBW rate occurred after the implementation of SBL in the total sample or stratified by city density tertiles or maternal age groups. Conclusion: SBL implementation did not show short-term impact on LBW rate in Chile. Further studies need to examine long-term impact of SBL on low birthweight.

Keywords: Chile; Latin America; low birth weight; maternal & child health; smoke-free policy; tobacco.

FIGURE 1

Sample selection flowchart. LBW: Low birth weight (birthweight <2,500 g), Chile, 2011–2015.

FIGURE 2

Time series of birth outcomes before and after the implementation of the smoking ban law in Chile stratified by maternal age group, 2011–2015. LBW: Low birth weight (birthweight <2,500 g), GA: Gestational age, SGA: Small for gestational age. Time was a discrete variable measured as 20 trimesters or quarters: from the first trimester of 2011 (time = 0 = 2011q1) to the last trimester of 2015 (time = 19 = 2015q4). The red line shows the implementation of the smoking ban law (trimester including March 2013 = 2013q1).

FIGURE 3

Effect of smoking ban law implementation over low birthweight rate in all 21 Chilean cities and by tertiles of city density, 2011–2015. LBW: Low birth weight (birthweight <2,500 g); IRR: Incidence Rate Ratio; 95% CI: 95% Confidence Interval. The top left figure shows the predicted LBW rate for all 21 Chilean cities; the top right figure shows the predicted LBW rate for cities of the lowest tertile of population density (≤6,153 pers/km²); the bottom left figure shows the predicted LBW rate for cities of the intermediate tertile of population density (6,198–8,132 persons/km²); the bottom right figure shows the predicted LBW rate for cities of the highest tertile of population density (≥8,134 persons/km²). Time was a discrete variable measured as 20 trimesters or quarters: from the first trimester of 2011 (time = 0 = 2011q1) to the last trimester of 2015 (time = 19 = 2015q4). The red line shows the implementation of the smoking ban law (trimester including March 2013 = 2013q1).

FIGURE 4

Effect of smoking ban law implementation over low birthweight rate in all 21 Chilean cities by maternal age group 2011-2015. LBW: Low birth weight (birthweight <2500 grams); IRR: Incidence Rate Ratio; 95% CI: 95% Confidence Interval. The top left figure shows the predicted LBW rate for mothers younger than 20 years old; the top right figure shows the predicted LBW rate for mothers between 20 and 34 years old; the bottom left figure shows the predicted LBW rate for mothers with 35 years or older. Time was a discrete variable measured as 20 quarters: from the first quarter or trimester of 2011 (time=0=2011q1) to the last quarter or trimester of 2015 (time=19=2015q4). The red line shows the implementation of the smoking ban law (March 2013).