The following conditions are necessary for pregnancy: First, the reproductive tract must be open: the male vas deferens must be open for the sperm to be discharged, and the female reproductive tract, including the vagina, cervix, uterus and fallopian tubes must be open so that the sperm entering the vagina during sex can reach the fallopian tubes without obstruction, meet and fertilize the egg, and the fertilized egg can enter the uterine cavity smoothly. If the fertilized egg enters the uterine cavity earlier or later, making the endometrium unsuitable for the fertilized egg’s implantation and development, it will be impossible to get pregnant. The woman should have a normal sex life before and after ovulation so that the sperm and egg can meet and fertilize and the ovaries can ovulate normally before pregnancy is possible.