We airbrush pregnant women all the time.
The active ingredient in airbrush tanning solution is the same active ingredient as in the over the counter self-tanners. It was approved for cosmetic use by the FDA in 1973.
If your Doctor has no objection to you using self-tanners while pregnant then your Doctor will likely have no objection to you being airbrushed with the same ingredient.
When you check with your Doctor, tell him or her that the active ingredient is dihydroxyacetone, the same active ingredient found in self tanners. (Spell dihydroxyacetone] Most in the medical profession are quite familiar with DHA. Some dermatologists and plastic surgeons even sell self-tanners containing DHA in their offices. If your doctor needs more information just let us know.