Are There Any Side Effects Of Taking Antibiotics And Birth Control Pill Together?

my girlfriend has been taking birth-control pills for almost 2 years now (Yasmin), and it's been 8 days since her period. She started taking some antibiotics (ciprofloxacin for an urine infection) 3 days ago. Today we had unprotected sexual relations, now we wonder if it's possible that she might get pregnant because of the effects of the antibiotoc. Thanks