Pap/pelvic exam during pregnancy

Can anyone tell me why this is necessary in pregnancy? I have really great medical care, but I spotted from sex or an ultrasound twice, and now I'm afraid for my doctor to do a pelvic exam/Pap smear. He didn't seem like he wanted to do it in the first trimester because I was spotting maybe, and I was wondering if it has any benefit for the baby or just me. Thank you!