All estimates were weighted. Age-adjusted estimates for nonpregnant women were calculated by direct standardization to the age distribution of pregnant women using the following weights: 0.269 (18-24 years), 0.569 (25-34 years), and 0.162 (35-44 years). Error bars indicate standard error.
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Liu B, Xu G, Rong S, et al. National Estimates of e-Cigarette Use Among Pregnant and Nonpregnant Women of Reproductive Age in the United States, 2014-2017. JAMA Pediatr. 2019;173(6):600–602. doi:10.1001/jamapediatrics.2019.0658
Pregnant women and developing fetuses are vulnerable to exposure to tobacco products. Some animal studies have shown that maternal use of electronic cigarettes (e-cigarettes) adversely affects offspring’s lung development1 and cognitive function.2 There is an urgent need for clinical and epidemiologic studies of e-cigarette use during pregnancy.3 Estimating the prevalence of e-cigarette use among pregnant women is critical to inform future research and policy. Previous studies3,4 have reported national prevalence of e-cigarette use among general adult populations. However, less is known about e-cigarette use in pregnant women. We used nationally representative data from the National Health Interview Survey (NHIS) to estimate the prevalence of e-cigarette and conventional cigarette use among pregnant women and nonpregnant women aged 18 to 44 years in the United States.
The NHIS is a nationally representative annual survey of the noninstitutionalized civilian US population. The NHIS collects information about health-related topics through household interviews. Women of reproductive age are also asked whether they are currently pregnant. The University of Iowa institutional review board determined that the current study was exempt from approval because of the use of deidentified data.
Since 2014, NHIS participants have been asked the following question about their lifetime use of e-cigarettes: “Have you ever used an e-cigarette, even one time?” Adults who answer in the affirmative are then asked, “Do you now use e-cigarettes every day, some days, or not at all?” Current use of e-cigarettes is defined as using e-cigarettes every day or some days. In addition, all participants are asked about their lifetime and current use of conventional cigarettes.
We estimated the prevalence of ever and current use of e-cigarettes and conventional cigarettes from 2014 to 2017, with survey weights to account for unequal probability of selection and nonresponse. We calculated age-adjusted estimates for nonpregnant women by direct standardization according to the age distribution of the sample of pregnant women.5 Differences were calculated using the Rao-Scott χ2 test with an adjusted F statistic. All data analyses were conducted using survey procedures in SAS 9.4 (SAS Institute). Two-sided P <.05 was considered statistically significant.
This analysis included 27 920 women aged 18 to 44 years (1071 pregnant women and 26 849 nonpregnant women). The weighted prevalence (standard error [SE]) of current conventional cigarette use was significantly lower among pregnant women (8.0% [2.4%]) than among nonpregnant women (14.3% [0.4%]; P = .01 for difference). However, the weighted prevalence (SE) of current e-cigarette use was not significantly different between pregnant women (3.6% [2.4%]) and nonpregnant women (3.3% [0.2%]; P = .92 for difference) (Figure 1). The prevalence of current e-cigarette use differed substantially by conventional cigarette smoking status (Figure 2). Among pregnant women, the weighted prevalence (SE) of current e-cigarette use was 38.9% (19.0%) among current conventional cigarette smokers, 1.3% (1.0%) among former smokers, and 0.3% (0.3%) among never smokers. Among nonpregnant women, the weighted prevalence of current e-cigarette user was 13.5% (0.8%) for current conventional cigarette smokers, 8.8% (1.0%) for former smokers, and 0.7% (0.1%) for never smokers.
Using data from a national leading health survey, this study provided the first national estimates of e-cigarette use among US pregnant women and nonpregnant women of reproductive age. Previous studies on the prevalence of e-cigarette use during pregnancy are sparse,3 and none of the previous studies was based on a nationally representative sample. In this study, although the prevalence of current conventional cigarette use was significantly lower in pregnant women than in nonpregnant women, the prevalence of current e-cigarette use was almost identical between pregnant and nonpregnant women.
The prevalence of current e-cigarette use was high among pregnant women who currently used conventional cigarettes. It is possible that some pregnant women perceived e-cigarettes as a safe alternative to conventional cigarettes. In addition, some women who used conventional cigarettes might have switched to e-cigarettes in pregnancy as a means of smoking cessation.6 A major limitation of this study is the limited sample size for pregnant women, although the overall sample size was large. As a result, the precision of the prevalence estimates among pregnant women may be limited. Further investigation with a larger sample size is warranted. Longitudinal studies starting from the preconception period are needed to determine the changing patterns in e-cigarette and conventional cigarette use among pregnant women.
Accepted for Publication: January 9, 2019.
Corresponding Author: Wei Bao, MD, PhD, Department of Epidemiology, College of Public Health, University of Iowa, 145 N Riverside Dr, Room S431 CPHB, Iowa City, IA 52242 (firstname.lastname@example.org).
Published Online: April 29, 2019. doi:10.1001/jamapediatrics.2019.0658
Author Contributions: Dr Bao had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.
Concept and design: Liu, D. Santillan, M. Santillan, Bao.
Acquisition, analysis, or interpretation of data: All authors.
Drafting of the manuscript: Liu, D. Santillan, M. Santillan, Bao.
Critical revision of the manuscript for important intellectual content: All authors.
Statistical analysis: Liu, M. Santillan, Bao.
Administrative, technical, or material support: D. Santillan, M. Santillan, Snetselaar, Bao.
Conflict of Interest Disclosures: None reported.
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