Abstract
Background. While active maternal tobacco smoking has well established adverse perinatal outcomes, the effects of passive maternal smoking, also called environmental tobacco exposure (ETS), are less well studied and less consistent. Objective: To determine to the effect of ETS on perinatal outcomes. Search strategy. Medline, EMBASE and reference lists were searched. Selection criteria. Studies comparing ETS-exposed pregnant women with those unexposed which adequately addressed active maternal smoking. Data collection and analysis. Two reviewers independently assessed titles, abstracts, full studies, extracted data and assessed quality. Dichotomous data were pooled using odds ratios (OR) and continuous data with weighted mean differences (WMD) using a random effects model. Main results. Seventy-six articles were included with a total of 48,439 ETS-exposed women and 90,918 unexposed women. ETS-exposed infants weighed less [WMD –60 g, 95% confidence interval (CI) –80 to –39 g], with a trend towards increased low birthweight (LBW, < 2,500 g; RR 1.16; 95% CI 0.99–1.36), although the duration of gestation and preterm delivery were similar (WMD 0.02 weeks, 95% CI –0.09 to 0.12 weeks and RR 1.07; 95% CI 0.93–1.22). ETS-exposed infants had longer infant lengths (1.75 cm; 95% CI 1.37–2.12 cm), increased risks of congenital anomalies (OR 1.17; 95% CI 1.03–1.34) and a trend towards smaller head circumferences (–0.11 cm; 95% CI –0.22 to 0.01 cm). Conclusions. ETS-exposed women have increased risks of infants with lower birthweight, congenital anomalies, longer lengths, and trends towards smaller head circumferences and LBW.
Acknowledgements
We gratefully acknowledge additional data and clarification provided by Drs. Mainous, Eskenazi, Lødrup Carlsen, Borlee, Chen, Hu, Krapels, Steegers, Meeker, Jaddoe, Bakker, Maconochie, Carmichael, Perera, Ekwo and Baker. We are indebted to our translators including Marc Colangelo, Ingrid McTiernan, Sophie Kuziora, Michal Bodhanovic, Mingyu Huang, Irena Szymanska, Katherine Morrison, Issei Nakamura, and Penka Stoyanova.
Declaration of interest: None of the authors have any financial or other conflict of interest. This study was supported by funding from the Canadian Institute of Health Research (CIHR) Knowledge Synthesis/Translation grant # KRS 86242. Dr. McDonald is supported by a CIHR New Investigator Award. CIHR did not have any role in the design, data collection, management, analysis, interpretation of the data, or preparation, review, or approval of the manuscript.
*Members of Knowledge Synthesis Group on determinants of low birth weight/preterm birth: Prakesh Shah, Associate Professor, Department of Paediatrics, Mount Sinai Hospital and Department of Health Policy, Management and Evaluation, University of Toronto, Toronto, Canada; Arne Ohlsson, Professor Emeritus, Department of Paediatrics, Mount Sinai Hospital, New York, USA, and Departments of Paediatrics, Obstetrics and Gynaecology, and Health Policy, Management and Evaluation, University of Toronto, Canada; Vibhuti Shah, Associate Professor, Department of Paediatrics, Mount Sinai Hospital, New York, USA, and Department of Health Policy, Management and Evaluation, University of Toronto, Toronto, Canada; Kellie E Murphy, Assistant Professor, Department of Obstetrics and Gynecology, Mount Sinai Hospital, New York, USA, and University of Toronto, Canada; Sarah D McDonald, Assistant Professor, Division of Maternal-Fetal Medicine, Departments of Obstetrics & Gynecology and Diagnostic Imaging, and Clinical Epidemiology & Biostatistics, McMaster University, Hamilton, Canada; Eileen Hutton, Associate Professor, Department of Obstetrics and Gynecology, McMaster University, Hamilton, Canada; Christine Newburn-Cook, Associate Professor & Associate Dean Research, Faculty of Nursing, University of Alberta, Edmonton, Canada; Corine Frick, Director, Alberta Perinatal Health Program and Adjunct Professor, Faculty of Nursing, University of Calgary, Calgary, Canada; Fran Scott, Associate Professor, Dalla Lana School of Public Health, University of Toronto and Toronto Public Health, Toronto, Canada; Victoria Allen, Associate Professor, Department of Obstetrics and Gynaecology, Dalhousie University, Halifax, Canada; Joseph Beyene, Associate Professor and Senior Scientist, Research Institute of The Hospital for Sick Children and Dalla Lana School of Public Health, University of Toronto, Toronto, Canada.