Safety period on the regular menstrual cycle women only have the so-called safety period, menstrual cycle irregular women do not have a safety period, irregular menstrual cycle, ovulation is irregular, ovulation irregularities lead to no specific safety period. If the menstrual cycle is about 28-30 days, is a regular menstrual cycle, the 1st menstruation, ovulation in about 10-20, except for 10-20, are safe period, coitus pregnancy chances are small, but not 100% will not be pregnant. When having intercourse during the safe period, due to sexual excitement stimulation, will lead to abnormal ovulation, causing pregnancy, women are not recommended to use the safe period contraception, should wear a condom contraception or take short-acting contraceptive pills or birth control ring.