Objective: to assess whether the two anti-tobacco laws enacted in Spain in 2006 and 2011 to reduce exposure to second-hand smoke were associated with a reduction in the frequency of preterm (PT) birth, low birth weight (LBW) and small for gestational age (SGA).
Design: cross-sectional population-based study. Data obtained from the national birth register of Spain through the Instituto Nacional de Estadística.
Population under study: 5 293 700 infants born alive at gestational ages between 22 and 44 weeks in Spain in the period ranging from January 2000 to December 2013.
Intervention: in January 2006 the first anti-tobacco law took effect, which banned smoking in workplaces except in the hospitality sector. In January 2011, an amendment of this law extended the prohibition to hospitality settings. The authors established three periods of study: pre-legislation (2000-2005), partial prohibition (2006-2010) and total prohibition (2011-2013).
Outcome measurement: primary variable: proportion of PT births (before 37 weeks’ gestation), LBW infants (< 2500 g) and SGA infants (birth weight below the 10th percentile).
Secondary variables: maternal age, socioeconomic status, place of birth, singleton or multiple birth, and place of residence.
Main results: of all infants born in the 2000-2013 period, 7.9% were born PT, 9.2% were SGA and 7.8% had a LBW. There was no information on the prevalence of smoking during pregnancy.
Based on raw proportions, the linear trend of preterm births was increasing and peaked between 2007 and 2009, descending moderately thereon. The low birth weight trend was on an increase in the pre-legislation and partial prohibition periods, and plateaued in the last 4 years under study. The proportion of SGA newborns remained more or less stable through time.
The percentages of the changes in proportions, calculated immediately and a year after the enactment of the partial and total bans, were:
Period of partial prohibition:
PT newborns: 4.6% increase (confidence interval [CI]: 2.9 to 6.2), sustained at 5.5% a year later (CI: 5.8 to 7.4).
LBW newborns: 0.6% increase (CI: -1 to 2.1), rising to 1.2% 1 year later (CI: -0.4 to 3).
SGA newborns: 4.9% reduction (CI: -6.2 to -3.5), maintained the year after (-4.2%).
Period of total prohibition:
PT newborns: 4.5% reduction (IC: -6.1 to -2.9) relative to the partial prohibition period, maintained a year later (-4.1%).
LBW newborns: 2.3% reduction (CI: -3.8 to -0.7), with a 3.5% decline 1 year later (CI: -5 to -2.1)
SGA newborns: 0.7% increase (CI: -0.8 to 2.2) and a 1.7% reduction the following year (-3.1 to -0.3).
Conclusion: in Spain, there has been a reduction in the risk of preterm births and low-birth-weight newborns coinciding with the enactment of anti-tobacco legislation, and especially with the total ban to smoking in work settings and indoor public spaces.
Conflicts of interest: none.
Funding source: FIS PI11/01276 grant of the Instituto de Salud Carlos III.