A 30-day menstrual cycle, menstruation on the 18th and intercourse on the 28th is not ovulation, but it is possible to get pregnant. Women’s menstrual pattern, ovulation is generally in the next menstrual day 14 days before the first day, and ovulation before 4 days and 5 days after the day plus the day of ovulation, a total of 10 days for the ovulation period. 18 menstruation, the day of ovulation for the 4th of the next month, ovulation for the 30th ~ 9, if the ovulation in the ovulation period of the coitus, the chances of conception is very large. The 28th is not considered to be ovulation, the chances of pregnancy are relatively small. However, ovulation is greatly affected by the surrounding environment, emotions and other influences, and unexpected ovulation may occur. For women who do not intend to get pregnant, it is important to take good contraceptive measures at every period to avoid the possibility of unintended pregnancy.