Smokefree laws reduce preterm births

Kristin Ashford, Ellen Hahn and their colleagues at the University of Kentucky recently published and important addition to the literature on the immediate health benefits of smokefree laws. Their paper ‘Municipal smoke-free laws and preterm birth Municipal smoke-free laws and preterm birth” cross-links 16 years of birth data in Kentucky to their database of local smoking restriction laws. They find that comprehensive, but not comprehensive, smoking restrictions are followed by a 9% drop in preterm birth after controlling for other know risk factors.

This paper is consistent with earlier work (Been et al, Ji et al) showing an association between smokefree laws and fewer complications of pregnancy.

This finding that comprehensive laws only had a positive effect on preterm birth is a first and is consistent with earlier work showing that stronger smoking restriction laws had bigger effects that weaker laws on hospital admissions for cardiovascular disease, stroke and respiratory disease.

Here is the abstract:

Background: Smoking during pregnancy and prenatal secondhand smoke exposure increase risk for preterm birth. As Kentucky has the second highest rate of smoking in the US and no statewide smoke-free law, examination of the impact of municipal smoke-free legislation on preterm birth is warranted.

Objective: This study used state-level live birth data and county-level municipal smoke-free legislation status to assess the association between presence and strength of smoke-free laws and the likelihood of preterm birth. We hypothesized that pregnant persons living in counties with comprehensive municipal smoke-free laws prohibiting smoking inside all workplaces and enclosed public places would exhibit lower likelihood of preterm birth compared with those living in counties with weak/moderate (i.e., smoke-free laws with exemptions that do not cover all workplaces and enclosed public places) or no smoke-free laws.

Study design: Using live birth data from the Kentucky Office of Vital Statistics with birth years ranging from 2004 – 2020 inclusive, a total of 894,372 live births were recorded that indicated the childbearing person was between the ages of 18 and 49 and a resident of Kentucky; these live births formed the sample for the study. Municipal ordinances implemented during a given calendar year were coded in the model as present starting with the following calendar year, since the birth records were time de-identified except for year of birth. This lagged law convention maximized the likelihood that pregnant persons included in the study were exposed to the smoke-free policy for at least a portion of their pregnancy. Multilevel logistic regression was used to assess the effect of smoke-free ordinances on likelihood of preterm birth, with personal- and county-level variables included as potential covariates and pregnant persons nested within county of residence. Data analysis was conducted using SAS, version 9.4, with an alpha of .05.

Results: Nearly all personal-level variables were associated with preterm birth status. Personal factors associated with an increased likelihood of preterm birth included being older (relative to 18-24 years old; odds ratios (95% confidence intervals) [ORs (CIs)]: 1.02 (1.01-1.04) and 1.27 (1.24-1.31) for 25-34 and 35-49, respectively); having a history of preterm birth (OR=4.65, CI: 4.53-4.78); and smoking prior to pregnancy (OR=1.14, CI: 1.12-1.16). Compared with pregnant persons living in counties without a smoke-free ordinance, those living in counties with comprehensive laws were 9% less likely to have a preterm birth (OR=0.91, CI: 0.89-0.94; p<.001). There was no difference in likelihood of preterm birth between those living in counties with moderate or weak laws compared with those unprotected by any smoke-free ordinance in their county of residence.

Conclusion: This study is among the first in the US to demonstrate comprehensive municipal smoke-free laws are associated with reduced risk for preterm birth, while moderate/weak smoke-free laws are not. These findings have major implications for public health policy and underscore the potential impact of health care providers’ advocacy for strong smoke-free policies, prohibiting smoking in all workplaces (including restaurants, bars, and casinos), to support healthy pregnancies.

Ashford KB, Blair LM, Mccubbin AK, Wiggins AT, Rayens MK, Hahn EJ. Municipal smoke-free laws and preterm birth. Am J Obstet Gynecol. 2022 Aug 3:S0002-9378(22)00627-5. doi: 10.1016/j.ajog.2022.07.058. Epub ahead of print. PMID: 35932874. It is available here.

Published by Stanton Glantz

Stanton Glantz is a retired Professor of Medicine who served on the University of California San Francisco faculty for 45 years. He conducts research on tobacco and cannabis control and cardiovascular disease/

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