Birth control and sex for the first time

I was talking with my friend about a friend who recently got married and now shes pregnant I was shocked too early obviously... and I asked was she on birth control and she said no its not safe to have birth control on ur first time. I feel like it makes no sense... its not my concern why they didnt take extra precautions but im here to ask if thats true or not? I mean why would it be "unsafe"?