Table 1  Themes of IHBM constructs and selected quotes related to risk perceptions of e-cigarette use during pregnancy in 25 online discussion threads, adapted by Schilling et al. 31 .

Identified themes of IHBM constructs	Selected quotes
[…] Smileys within the text/aspects added by the researcher for clarification. T = number of the associated thread; year of the post.
Perceived threats
Severe nicotine-related health risks (a)	“Nicotine is an addictive drug and a neurotoxin, which of course can be transmitted to the unborn child. Thatʼs why I would personally abstain from nicotine during pregnancy!” (T20, 2017)
Potential health risks of additional ingredients (b)	“Even if you smoke without nicotine, there are toxins that are not good for your lungs and certainly not for the baby.” (T11, 2016)
Relative risks (c)	“Whether it is harmful to the child has not been proven yet, but what has been proven is that it is healthier, contains 3800 fewer toxins and you cannot smoke passively, etc.” (T5, 2012)
Lack of knowledge and research studies (d)	“Even those without nicotine contain chemicals and nobody knows what the long-term consequences will be!” (T3, 2012)
Perceived benefits
Harm reduction (e)	“Vaping without nicotine is 10 times better than smoking. But of course, you should not vape during pregnancy either. But vaping is an option to move away from normal cigarettes towards no cigarettes.” (T1, 2011)
Possibility and facilitation of smoking cessation (f)	“Yes, I had already thought about e-cigarettes. It would be ideal, the habit stays, but thereʼs no more nicotine.” (T7, 2014)
Financial benefits (g)	“Good luck to anyone who wants to live healthier and wants to save a lot of money at the same time.” (T2, 2011)
Perceived barriers
Lack of satisfaction (h)	“Although I donʼt smoke, cigarettes without nicotine, isnʼt that like drinking without alcohol? – Do you think that will satisfy your cravings?” (T22, 2012)
Social stigma (i)	“I would say ‘stop that’ [e-cigarette use during pregnancy] is the general answer. [Evil smiley] Be happy you havenʼt been put through the wringer yet!” (T11, 2016)
Attitudes
Negative attitudes (j)	“As far as I know, this alternative to ‘normal’ smoking is very controversial. In my opinion, one should completely leave it alone during pregnancy!” (T15, 2017)
Positive attitudes (k)	“It is certain that not vaping or smoking is always better! […] But vaping without nicotine is still 1000 times better than smoking! ” (T17, 2011)
Perceived norms
Attitudes and behavior in the social environment (l)	“My husband is a chemist and looked at the ingredients. He says thatʼs a good alternative for pregnant women.” (T11, 2016)
Recommendations of medical providers (m)	“Hey, in my last pregnancy, I could not stop that s*** smoking, therefore the chief physician in the hospital recommended that I use e-cigarettes without nicotine, stating that it is healthier than normal cigarettes.” (T11, 2016)