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. Hormonal imbalance, stress, certain medications as contraceptives, polycystic ovarian syndrome, eating disorders, vigorous exercise and thyroid disorders, could also cause delayed period.