Methodological Concerns about a Systematic Review and Meta-analysis of Maternal Active Smoking during Pregnancy and Low Birth Weight

Methodological Concerns about a Systematic Review and Meta-analysis of Maternal Active Smoking... Nicotine & Tobacco Research, 2018, 1–1 doi:10.1093/ntr/nty015 Letter Letter Methodological Concerns about a Systematic Review and Meta-analysis of Maternal Active Smoking during Pregnancy and Low Birth Weight Bing-Kun Zheng Master of Science in Nursing, MSN, Na Li Master of Science in Nursing, MSN Neonatal Intensive Care Unit, First Affiliated Hospital of Zhengzhou University, Zhengzhou, China Corresponding Author: Na Li, Master of Science in Nursing, MSN, Neonatal Intensive Care Unit, First Affiliated Hospital of Zhengzhou University, Zhengzhou, China, 130021, Tel +86 18703829016, E-mail: yxy0822@126.com. We read with interest the article by Pereira et al. in a recent issue However, an opposite association was found after adjustment for of Nicotine & Tobacco Research. The authors investigated the rela- potential confounders (odds ratio = 0.95). Therefore, to objectively tionship between maternal active smoking during pregnancy and appreciate the relationship between maternal active smoking during low birth weight in the Americas through a systematic review and pregnancy and low birth weight, the authors should at least consider meta-analysis. The pooled analysis showed that active maternal reporting a separate analysis using adjusted odds ratios. smoking was significantly associated with low birth weight (odds ratio  =  2.00; 95% confidence interval  =  1.77–2.26). We have con- Funding cerns about several methodological issues that may compromise the None declared. inferences of this study. First, active smoking during pregnancy was not defined. The authors need to clarify the minimum amount of tobacco consumed Declaration of Interests per day that can be defined as active smoking in this review. It would None declared. be helpful for readers if the specific definitions of active smoking in different included studies were presented. Second, we understand that it was not possible to stratify the Acknowledgments meta-analysis by frequency and quantity of tobacco consumption None declared. because of different methods of categorization. However, as men- tioned by the authors, information about the number of smoked cigarettes per day was categorized in seven studies. A thorough nar- References rative synthesis of evidence regarding the effect of different quantities 1. Pereira PP, Da Mata FA, Figueiredo AC, de Andrade KR, Pereira MG. of tobacco consumption on birth weight is feasible and necessary. Maternal active smoking during pregnancy and low birth weight in Last, only 14 of 34 included studies reported measurement of the americas: a systematic review and meta-analysis. Nicotine Tob Res. data (ie, odds ratios and 95% confidence intervals) that adjusted 2017;19(5):497–505. for potential confounders. It seems that only unadjusted odds ratios 2. von Elm E, Altman DG, Egger M, et al. The strengthening the reporting of were chosen to perform the pooled analysis when both adjusted observational studies in epidemiology (STROBE) statement: guidelines for and unadjusted odds ratios were available. That is problematic reporting observational studies. Lancet. 2007;370(9596):1453–1457. because adjustment for potential confounders is very important in 3. Moliterno LF, Monteiro B, Figueredo CM, Fischer RG. Association an observational study. For example, one of the included studies by between periodontitis and low birth weight: a case-control study. J Clin Moliterno et al. showed that the unadjusted odds ratio was 1.16. Periodontol. 2005;32(8):886–890. © The Author(s) 2018. Published by Oxford University Press on behalf of the Society for Research on Nicotine and Tobacco. All rights reserved. 1 For permissions, please e-mail: journals.permissions@oup.com. Downloaded from https://academic.oup.com/ntr/advance-article-abstract/doi/10.1093/ntr/nty015/4821020 by Ed 'DeepDyve' Gillespie user on 08 June 2018 http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Nicotine and Tobacco Research Oxford University Press

Methodological Concerns about a Systematic Review and Meta-analysis of Maternal Active Smoking during Pregnancy and Low Birth Weight

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Oxford University Press
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© The Author(s) 2018. Published by Oxford University Press on behalf of the Society for Research on Nicotine and Tobacco. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.
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10.1093/ntr/nty015
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Abstract

Nicotine & Tobacco Research, 2018, 1–1 doi:10.1093/ntr/nty015 Letter Letter Methodological Concerns about a Systematic Review and Meta-analysis of Maternal Active Smoking during Pregnancy and Low Birth Weight Bing-Kun Zheng Master of Science in Nursing, MSN, Na Li Master of Science in Nursing, MSN Neonatal Intensive Care Unit, First Affiliated Hospital of Zhengzhou University, Zhengzhou, China Corresponding Author: Na Li, Master of Science in Nursing, MSN, Neonatal Intensive Care Unit, First Affiliated Hospital of Zhengzhou University, Zhengzhou, China, 130021, Tel +86 18703829016, E-mail: yxy0822@126.com. We read with interest the article by Pereira et al. in a recent issue However, an opposite association was found after adjustment for of Nicotine & Tobacco Research. The authors investigated the rela- potential confounders (odds ratio = 0.95). Therefore, to objectively tionship between maternal active smoking during pregnancy and appreciate the relationship between maternal active smoking during low birth weight in the Americas through a systematic review and pregnancy and low birth weight, the authors should at least consider meta-analysis. The pooled analysis showed that active maternal reporting a separate analysis using adjusted odds ratios. smoking was significantly associated with low birth weight (odds ratio  =  2.00; 95% confidence interval  =  1.77–2.26). We have con- Funding cerns about several methodological issues that may compromise the None declared. inferences of this study. First, active smoking during pregnancy was not defined. The authors need to clarify the minimum amount of tobacco consumed Declaration of Interests per day that can be defined as active smoking in this review. It would None declared. be helpful for readers if the specific definitions of active smoking in different included studies were presented. Second, we understand that it was not possible to stratify the Acknowledgments meta-analysis by frequency and quantity of tobacco consumption None declared. because of different methods of categorization. However, as men- tioned by the authors, information about the number of smoked cigarettes per day was categorized in seven studies. A thorough nar- References rative synthesis of evidence regarding the effect of different quantities 1. Pereira PP, Da Mata FA, Figueiredo AC, de Andrade KR, Pereira MG. of tobacco consumption on birth weight is feasible and necessary. Maternal active smoking during pregnancy and low birth weight in Last, only 14 of 34 included studies reported measurement of the americas: a systematic review and meta-analysis. Nicotine Tob Res. data (ie, odds ratios and 95% confidence intervals) that adjusted 2017;19(5):497–505. for potential confounders. It seems that only unadjusted odds ratios 2. von Elm E, Altman DG, Egger M, et al. The strengthening the reporting of were chosen to perform the pooled analysis when both adjusted observational studies in epidemiology (STROBE) statement: guidelines for and unadjusted odds ratios were available. That is problematic reporting observational studies. Lancet. 2007;370(9596):1453–1457. because adjustment for potential confounders is very important in 3. Moliterno LF, Monteiro B, Figueredo CM, Fischer RG. Association an observational study. For example, one of the included studies by between periodontitis and low birth weight: a case-control study. J Clin Moliterno et al. showed that the unadjusted odds ratio was 1.16. Periodontol. 2005;32(8):886–890. © The Author(s) 2018. Published by Oxford University Press on behalf of the Society for Research on Nicotine and Tobacco. All rights reserved. 1 For permissions, please e-mail: journals.permissions@oup.com. Downloaded from https://academic.oup.com/ntr/advance-article-abstract/doi/10.1093/ntr/nty015/4821020 by Ed 'DeepDyve' Gillespie user on 08 June 2018

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Nicotine and Tobacco ResearchOxford University Press

Published: Jan 23, 2018

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