Is it safe to be exposed to second-hand smoke while pregnant?

No. Home is the main place I suggest that pregnant women tell friends/family to "take it outside" if people smoke they not only make themselves unhealthy (affecting financially those who depend on them) but also sicken pregnant women and predispose the babies to be smaller both before and after birth. If smokers want to be part of the life of families they say they love they should stop smoking asap!
No. Unfortunately, we now know that second-hand smoke is unsafe for everyone, pregnant or not! It is safe to say that avoiding second-hand smoke while pregnant is wise - avoid smoky cars, bars and restaurants. However, the message here is not to imply that one exposure will cause permanent damage to your baby. In the long run, the best idea is to avoid exposure as much as you can.