Fertilization is a complex physiological process that can occur only during ovulation. The ripened egg lives for very long – just a few hours, the sperm in this respect is much tougher. There were times when fertilization occurred a week after intercourse.But often the couple can't wait to conception for a long time, even several years. Then you have to figure out why no fertilization occurs. All the causes can be divided into three groups: problems of female reproductive system problems of the male reproductive system, and immunological incompatibility between partners. Fertilization is impossible, if women in the menstrual cycle no ovulation, i.e. the egg is not formed, or cannot get from the ovary, for example, due to inflammation of its walls. Violation of menstruation are often associated with stress, hormonal imbalance, insufficient, or, conversely, overweight disease. Also the egg may unite with a sperm, but don't get into the uterus due to obstruction of the fallopian tubes or a violation of their contractile activity. In the latter case often develops ectopic pregnancy. Problems with the male reproductive system it is easier to detect but harder to cure. The sperm must be mobile, survivable, there must be a sufficient number. If the active half of them or less, that are diagnosed with infertility. But the reasons for that sperm quality is difficult to establish. In addition, fertilization may not occur due to violation of ejaculation men.It happens that the couple is healthy but to conceive this baby she is not successful. This is because the partners are incompatible in immunological parameters. A woman's body does not accept sperm particular man, against her producing special antibodies. The sperm die before reaching the uterus. The reasons for this phenomenon are unknown.