Is it safe to use a self-tanner during pregnancy?
No one knows, especially since it's hard to get women to line up for a study to see if something would hurt their babies. Until that time,
YOU'RE the study, which probably isn't very comforting.
If it's the dye-type spray, this is probably harmless, which is my humble opinion not based on any reputable (or otherwise!) study. If it's the type that gets melanocytes movin', this would make me nervous, sine you're messing with glandular stimulation.