The day of ovulation is usually the 14th day before the next menstrual period, five days before ovulation and four days after ovulation, we call the ovulation period, in the ovulation period coitus fertilization rate will be significantly higher. However, the success rate of using ovulation as a method of contraception is very low. Because the sperm can survive in the vagina for several days, for example, a few days before ovulation, then ovulation in advance, the sperm may still survive in the vagina, until ovulation and the egg combined to form a fertilized egg, which will lead to conception. So if you are going to take ovulation contraception women must pay more attention, because there is a possibility of contraceptive failure, so if the next menstrual period has not come, delayed for more than 7 days, you should buy your own pregnancy test to detect whether pregnancy.