Introduction:
The prevalence of electronic cigarette (ecigs) use has increased dramatically in recent years, possibly due to the promotion by industry and the advocacy of some physicians which suggest ecigs as a “safer” alternative to tobacco during pregnancy. Evidence suggests that studies in favor of ecigs are more likely to be funded by industry and this could influence physicians’ recommendations. Our aim is to describe the studies conducted on ecigs during pregnancy, with emphasis on conflicts of interest (COI).

Material and Methods:
We conducted a systematic literature search in PubMed to identify original articles on pregnant or postpartum women, published between 1/1/16-21/1/23, which analyzed the use of ecigs during pregnancy. The characteristics of the studies were collected, and a descriptive synthesis of the results was made. The conclusions (in favor, against, neutral) and the COI of the studies were assessed. We also evaluated their quality.

Results:
The search yielded 193 results, and 23 were selected for full-text reading. 15 original articles were included: 4 qualitative and 11 cross-sectional studies. The studies had between 2-14 authors, and were conducted in the UK (5/15), the USA (9/15) and Australia (1/15). The median quality score was 6 out of 10. Of the 15 studies, 12 had a COI section and, of these, 7/12 acknowledged potential COI (4 with the pharmaceutical industry, 1 with the ecigs industry, 1 with a consumer engagement company and 1 with a journal). Of the 15 studies, 10 received funding (1 from the pharmaceutical industry, 3 from a university, 8 from public bodies and 2 from a charitable association). Authors of 5 studies reported financial ties with the pharmaceutical industry and one with both the pharmaceutical and ecig industries. Of the studies declaring a COI with industry (5), 1 was against ecigs benefit (the COI was posterior to the study), 2 were in favor, and 2 were neutral. Of those without COI with industry (10), 3 were against a benefit, 3 were in favor and 4 remained neutral.

Conclusions:
The results are unclear about the relation between the presence of COI and the conclusions, however the number of studies on ecigs during pregnancy is limited. In any case, health professionals should be aware of the existence of COI when interpreting the results of these studies, as they may be influenced by industry.