Is a chest x-ray safe while pregnant? in second trimester? is a protective cover necessary on stomach? they didn't cover my belly.

Yes: One chest x-ray is unlikely to cause harm. Radiation has it's greatest effect on a fetus during first trimester when organs are developing. Cosmic radiation of flying across the country is equivalent to about half the radiation dose of a chest x-ray. So flying from seattle to ny and back you essentially receive the same radiation as a chest x-ray. A shield is generally used during a chest x-ray.