It depends on the timing...if I need to yes I do...I am trying to recall the earliest I've done it...think it was when they were a couple weeks along. If the months up...then it's up, and I reapply. I keep them off the smear on her neck for several days...they usually congregate around her teats anyhow lol.
From their website...
11. Do the FRONTLINE Brand Products have any additional label claims?
Effective May 2003, FRONTLINE Plus and FRONTLINE Top Spot were approved by the Environmental Protection Agency (EPA) to be used on pregnant, lactating and breeding dogs and cats. FRONTLINE Spray is not approved to be used on pregnant, lactating and breeding dogs and cats. In addition, FRONTLINE Plus small size that was initially labeled for 11-22 lb dogs has now been approved for the use on any size dog up to 22 lbs