Age is one of the factors that has the most influence on the success rates of artificial insemination. Not only for the artificial insemination itself or for the number and/or quality of the oocytes (ovarian reserve), but also for the endometrium, since achieving the adequate thickness for the embryo to be able to implant becomes more complicated.
After the age of 35, the ovarian reserve decreases and, therefore, the probability of an egg being fertilized by a sperm is significantly reduced, especially after the age of 40.
Insemination is not recommended after the age of 35-37, since the probability of pregnancy is so low (less than 10%) that it is not worthwhile for the patient to go through the whole process. In these cases, in vitro fertilization is directly recommended.