This question about BOTOX during pregnancy or after giving birth is asked very frequently on AHB.
Most doctors agree that you can have BOTOX immediately after you are done breast feeding. Unfortunately, BOTOX isn't approved for use (or advised) during pregnancy or while nursing.
The following video by Dr. Carlos Wolf of Miami Plastic Surgery explains the BOTOX process and features a woman having BOTOX for the first time since she was pregnant. In the video, the procedure is described like a non-surgical browlift.