UTI as such does not delay periods. Pregnancy is the most common cause of absence of menstruation (amenorrhea). It is most likely if intercourse occurs anywhere from 3 days before ovulation (release of egg from the ovary) until 2-3 days after ovulation. If you did not have intercourse during that time of your menstrual cycle (12 to 16 days prior to your 1st day of expected period, its unlikely that you are pregnant.