Objective: To carry out a systematic literature reviews to clarify which are the main factors that hinder pregnancy by artificial insemination in sheep. Selection of articles: Articles related to morphometric parameters, AI techniques that go through the cervix (IAV, IAC, IATC) and laparoscopic AI, ways to preserve semen (fresh, refrigerated and frozen-thawed) and heat synchronization protocols , that within their results determine fertility, pregnancy or childbirth rates. Exclusion criteria: Articles written in languages other than Spanish, Portuguese and English, with species other than sheep, which do not describe the synchronization protocol, the presentation of the semen, the type of AI technique used, within its methodology and results. Fertility, pregnancy or childbirth rates, and items for which you would have to pay. Results: We selected 52 articles that met the inclusion criteria, of which 16 were related to morphometric parameters, cervical os and its correlation with age, and 36 were related to AI techniques, type of semen conservation, synchronization protocols and their correlation with fertility, pregnancy and calving rates. Conclusion: This work made it possible to clarify that the main factors that make pregnancy difficult for AI in sheep are the age of the animals, the morphometric parameters of the cervix, the type of AI technique and the presentation of the semen.