I think many Obs are recommending nicotine replacement for pregnant mothers who are smokers these days. I don't know if they recommend vaping or not.
I'd have to think that nicotine alone would be less harmful for a gestating fetus than smoking cigarettes, although I actually haven't seen any studies about it (although I have not looiked). It would be a good indicator if such a study were done, although I'm not sure it can be done, ethically, since it might "affect" a person's desire to quit or not. (I'm kind of thinking young, pregnant person who is a smoker, placed in a control group, etc.) Maybe there's someone collecting aggregate data.... Wait,the NIH did one:
Nicotine Gum for Pregnant Smokers: A Randomized Controlled Trial
Basically, there were statistically significant differences between neonatal scores and birth weight and maybe gestational length, the non-smoking moms were more likely to stay in the study, and slightly more likely to quit NRT altogether, were some of the main conclusions. I think. Need more coffee.
Anna