Sex during your period itself is fine and cannot cause problems for you. This is a myth perhaps perpetuated by religious beliefs that tend toward not touching a woman while she's on her period.
Definitely no !!
During the monthly period , the woman can't get pregnant even if she had sex . However having sex in that period may cause very serious problems to her , so always avoid having sex during the monthly period .
Always use protection. While it's unlikely, it can still happen depending when you ovulate as sperm can live inside you for 3-5 days. If you happen to be an early ovulator, that would be all it would take.