After ovulation of the follicle, if the oocyte does not meet a sperm, the remainder develops into the corpus luteum, which maintains activity for about 14 days and then disappears. If the oocyte combines with a sperm to form a fertilized egg, the corpus luteum disappears after 3 to 4 months. Every month, a follicle in one side of the ovary will discharge an egg cell into the peritoneal cavity, the egg cell if there is no encounter with the sperm, the remaining part of the follicle outside the corpus luteum develops into the corpus luteum, which disappears after 14 days of ovulation; if the egg cell is encountered with sperm, the corpus luteum will continue to play a role in the corpus luteum of pregnancy will continue to play a role in the corpus luteum of pregnancy, until 3-4 months of pregnancy, the placenta completely take over its role in the future after the disappearance of the corpus luteum. The life of the egg cell is relatively short, survival time is only 12 to 48 hours on average, therefore, for the preparation of the demand for women, only in the ovulation before and after 1 to 2 days of intercourse, the possibility of pregnancy is relatively large.