Prenatal exposure to second hand smoke and adverse perinatal outcomes
- Correspondence to Kristin B Ashford
Department of Nursing, #417 CON Building, University of Kentucky, Lexington, KY 40514, USA;
Implications for practice and research
■ Consistent and valid prenatal screening methods are necessary to document accurate exposure rates to second hand smoke (SHS).
■ Preconceptual parental education regarding the effects of prenatal exposure to SHS could contribute to a reduction in adverse perinatal outcomes.
■ Future research should consider using biochemical markers to determine exposure.
The science is clear that maternal tobacco use during pregnancy has adverse effects on acute and long-term perinatal outcomes. However, evidence regarding outcomes of prenatal SHS exposure is less clear. This study aims to evaluate the effects of SHS on a multitude of perinatal outcomes in women in Atlantic Canada.
Crane et al retrospectively analysed results from a large cohort (n=11 852) of pregnant women using a computerised database to evaluate prenatal SHS exposure on select outcomes. Non-smoking women with singleton gestation were included. SHS exposure was based on maternal self-report during the first trimester. Data were analysed using descriptive statistics, univariate analyses and regression models.
The final sample comprised 1202 women exposed and 10 650 not exposed to SHS. Generally, women exposed to SHS were younger, less educated and more likely to have comorbidities or use illicit drug and alcohol. The authors concluded that prenatal SHS exposure contributes to decreased birthweight, birth length, head circumference and increased incidence of stillbirth, preterm birth (<34 weeks gestation) and bacterial sepsis in the infant.
Consistent with a large body of evidence and a recent meta-analysis,1,3 this paper confirms the association between prenatal SHS exposure and increased risk for decreased birthweight, smaller head circumference, stillbirth and preterm birth (<34 weeks). Reductions in birthweight (−53 g) and head circumference (−0.24 cm) between those exposed and not exposed to SHS are comparable with several other recent reports.1
Strengths of this paper include evaluation of stillbirth, use of two preterm time points (<34, <37 weeks gestation), large sample size and comprehensive control of potential confounders in regression analyses. The present study adds to the evidence affirming the relationship between prenatal SHS exposure and stillbirth. Uniquely, the authors examine preterm birth in two contexts, which may lead to a more definitive association between SHS exposure and preterm birth at key gestational time points. In this large sample, standard (age, gravity/parity education, partnered status, work) and less used (body mass index, three weight categories, alcohol/drug use, comorbidities) variables were included in the data analysis. Control for these confounders adds strength to the associations.
In this study, nearly the entire sample was Caucasian (99%), which may limit generalisability.4 Although self-report of smoking status is seen as acceptable in large samples,1 biochemical validation (via urine, hair, serum) is a more accurate and objective measure when confirming smoking/exposure status in pregnant women.2 Understandably, high costs often deter researchers from collecting biomarkers. Although not assessed in this study, exposure source and quantification of exposure provide a more precise measure of SHS exposure.5
To ignore the increasing evidence that prenatal exposure to SHS contributes to adverse perinatal outcomes for both mother and infant would be irresponsible. Prevention strategies including parental preconceptual/prenatal education and focused public media campaigns on the harmful effects of SHS exposure are necessary to reduce and have an impact on perinatal-associated morbidity and mortality.