It is completely understandable to feel anxious about this. Taking the i-pill (levonorgestrel) can temporarily alter the menstrual cycle. Typically, it may cause the next period to be early, on time, or delayed by up to a week (7 days). If her period is delayed by more than 7 days, it is best to take a home pregnancy test to be sure. If you both have further concerns, consulting a doctor can offer peace of mind.