Hello dear I understand your concern Withdrawal method can cause pregnancy if you had sex in fertile phase of the period Withdrawal method is not successful in preventing the pregnancy as precum release in the vagina unknowingly before the ejaculation. (precum contain sufficient sperm that cause pregnancy). But you have taken Morning after pill with in 24 hours, It will highly effective in preventing the pregnancy. It has just 0-3% failure rate. So i think chance of pregnancy is very less according to you age. But your period may be delayed (1-2 week)/earlier and associated with excessive bleeding as pill cause hormonal imbalance. Avoid stress,take healthy diet, drink plenty of water and do regular exercise. If period become irregular then consult the gynecologist for examination. Hope this may help you Contact HCM for further health query Best regards Dr. Sagar