Impact of Smoke-free laws on Preterm Birth

Kristin Ashford, PhD, APRN

Joyce Robl, EdD, MS, CGC

Ruth Ann Shepherd, MD, FAAP

Presenter Disclosures

The following personal financial relationships with commercial interests relevant to this presentation

existed during the past 12 months

No relationships to disclose

Background

The unintended health consequences of primary and secondhand smoke (SHS) exposure on adults and children are evident.

There is no safe level of SHS (Surgeon General, 2006)

SHS contains approximately 4,000 chemicals, is responsible for nearly 3,000 cases of lung cancer deaths among nonsmokers each year, and affects more than 22 million US children annually (Surgeon General, 2006).

A growing body of evidence and two recent meta-analyses support the associations between SHS and increased risk for low birth weight, smaller head circumference, stillbirth and preterm birth (Ashford et al., 2010, Hegaard et al., 2006, CDC, 2006, Salmasi et al., 2010, Leonardi-Bee et al., 2011).

Nonsmoking pregnant women exposed to SHS smoke have a 23% higher risk for stillbirth and 13% more likely to have a child with a congenital malformation (Leonardi-Bee et al., 2011).

Smokefree Laws and Perinatal Health

First US report on the effects of city-wide smoking ban on perinatal health was conducted in Pueblo, Colorado

(Page et al., 2012)

•Enacted July 1st 2003•Significant reductions in maternal smoking (38%): preterm birth (23%)

US State-Specific Smoking Bans

International Smokefree Laws and Perinatal Health

Ireland (2004): first country to adopted a comprehensive country-wide smoke-free policy

Italy (2005): significant reductions in first and SHS exposure

Scotland (2006) enacted the Smoking, Health and Social Care Bill prohibiting smoking in all enclosed public places (Mackay et al., 2012).

Preterm Delivery, Spontaneous Preterm Labor, Small for gestational age (SGA)

Spain reported a significant decrease in infants exposed to SHS during pregnancy following a comprehensive public ban (Puig et al., 2012).

China: nonsmoking pregnant women whose husbands were smokers reported increased exposure to SHS in home following smoke-free policy (Yao et al., 2009)

Purpose

To determine the impact of smoke-free laws on three key perinatal outcomes in Kentucky communities that have adopted legislation to ban public smoking:

1)community risk for preterm birth (PTB)

2)smoking prior to pregnancy (PRIOR)

3)low birth weight (LBW)

Secondary Aim: To determine the impact of strength

of smokefree law on perinatal outcomes

Methods

This study used Kentucky live birth certificate files from 2004 to 2009 in Kentucky counties/cities with smoke-free laws/ordinances.

Records were classified into pre-law and post-law based on at least one year prior to and after implementation, respectively with exclusion of implementation years.

Laws with smoke-free enclosed public places were classified as strong (smoke-free enclosed public places) or weak (significant exemptions).

Non-singleton births were excluded from the analyses.

Data Analysis

Descriptive demographic statistics

Chi square analyses compared the births pre-and post-law.

Multivariable logistic regressions were completed to relate LBW, PTB and PRIOR to ordinance timing, strength of law, and demographic explanatory variables.

All analyses were completed using SAS version 9.2

Sample Demographic Characteristics N=75,234 live birth certificate records

Characteristic N (%)

Age

<20 years 8,307 (11.1%)

20-24 years 20,260 (26.9%)

25-29 years 22,043 (29.3%)

30-34 years 16,102 (21.4%)

≥35 years 8,498 (11.3%)

Race

White 55,977 (74.5%)

Black 14,242 (18.9%)

Other 4,961 (6.6%)

Payor Source

Medicaid 25,537 (34.2%)

Private 37,694 (50.4%)

Other 11,517 (15.4%)

Demographic CharacteristicsCharacteristic N (%)

Ethnicity

Non-Hispanic 69,836 (92.9%)

Hispanic 5,356 (7.1%)

Maternal Education

Less than High School

14,195 (19.1%)

High School 17,158 (23.0%)

Greater than High School

43,129 (57.9%)

Marital Status

Married 43,927 (58.4%)

Unmarried 31,293 (41.6%)

Results

 

Prior to Ordinance

%

Post Ordinance

%

p-value

Low Birth Weight 7.44% 7.15% 0.1306

Preterm Birth 10.7% 9.23% 0.0001*

Smoking Prior to Pregnancy (PRIOR)

23.80% 19.46% <0.0001*

Chi-square Analyses for Perinatal Outcomes

(Significance p < .05*)

Results

* significance level p < .05

Covariates in the Logistic Regression: Age, Race, Ethnicity, Education, Marital Status, Payor Source, Strength of Law

Adjusted Odds Ratios

Low Birth Weight 0.99 (0.93-1.06)

Preterm Birth 0.88 (0.83-0.93)*

PRIOR 0.77 (0.75-0.80)*

Results

Significant reductions in PTB and PRIOR were observed in communities post-law compared to pre-law (p <.0001). Births after implementation had reduced odds for PTB [Estimated Odds Ratio 0.87 (95% Confidence Interval 0.83-0.93)] and PRIOR [0.76 (0.73-0.79)].

Comprehensive strong laws demonstrated reduced odds for PTB [0.94 (0.88-0.997) and PRIOR [0.94 (0.90-0.99) compared to weak laws when controlling for the other variables.

Overall, there were no significant associations identified for LBW.

Limitations

Self report via Live Birth Certificate Records

Self report of smoking during perinatal period may not be reliable due to high deception rates

Lack of biomarker validation of smoking status

Discussion

This is one of the first studies in the US to examine the impact of large scale, community-based smoke-free laws on perinatal health outcomes.

Our study was consistent with the initial US report regarding significant reductions in PTB.

Communities can reduce smoking before pregnancy, reduce SHS to pregnant women and children, and decrease preterm birth rates through sustained and comprehensive smoke-free policies.

Strength of smoke-free policy positively impacts preterm birth and smoking three months prior to pregnancy rates when compared to less stringent laws that allow smoking exemptions.

QuestionsContact: Kristin.Ashford.uky.edu

University of Kentucky College of Nursing