In general, the length of cohabitation has no necessary relationship with pregnancy, not a positive correlation. Under normal circumstances, if both men and women are healthy, male sperm quality, sperm activity is good, the female body reproductive organs develop normally, the fallopian tubes are open, the ovaries can normally ovulate, in the ovulation period after intercourse will occur most of the natural pregnancy, and the length of cohabitation is not related. On the contrary, if the male sperm quality is poor, sperm activity is low, the female fallopian tube is not smooth, blocked, the egg can not be normal ovulation, the uterine lining is not suitable for fertilization of the egg, growth and development, both men and women’s mental stress, the cohabitation of a long time will not lead to female pregnancy. Therefore, if a woman wants to get pregnant and have children, it is best to have a pre-pregnancy physical examination to adjust the body to an ideal level, which will improve the conception rate.