When a woman experiences withdrawal bleeding, pregnancy usually does not occur, but in rare cases it can. Withdrawal bleeding occurs mainly due to the use of emergency contraceptive pills. If emergency contraception is taken before ovulation, the amount of withdrawal bleeding is small, the effect of the drug will disappear after a few days, and the uterine lining will still grow. If sex occurs during this period, ovulation occurs, so women can also lead to pregnancy, but the chances are less. Therefore, when a woman has withdrawal bleeding, but there is a delay in menstruation, or a woman has nausea, vomiting, fatigue, weakness and other discomforts, it is also necessary to go to the hospital to take a blood test of chorionic gonadotropin levels to rule out the occurrence of pregnancy.