It is safest to have intercourse during the safe period when you are not likely to get pregnant, but it cannot be completely ruled out that you will not get pregnant. The prerequisite for pregnancy is the need for a sperm to combine with an egg, and the only time in a month that an egg has a chance to be discharged is during ovulation. Ovulation is the 14th day before the next menstrual period, in order to be on the safe side, usually will be the day before 5 days and after 4 days are called ovulation, in the ovulation period coitus is the greatest chance of pregnancy. In addition to ovulation and menstruation, the rest of the month is the safe period, the chances of getting pregnant during the safe period are relatively low, so it is safest to have intercourse during the safe period when it is not easy to get pregnant. However, because the ovulation period will be affected by a variety of factors in life and some advance or push back, so the safe period is not absolutely safe, there will be a chance of pregnancy exists, do not want to get pregnant the best every time you have sex with a good contraceptive measures.