Conjunction (conjugated twins) is a malformation of monozygotic twins, described in human and many animal species. Its essence is the lack of a complete separation of twin organisms in the period of prenatal development as well as conjunction in various body parts. Etiology of this phenomenon has not been fully examined yet. Its main causes are environment pollution or the problem both in medicine and veterinary. The aim of this manuscript is to review research results on account of a growing number of conjunction cases as well as drawing attention to the correlation between this abnormality and a growing number of twin births. It is also crucial to present connections between an alarming increase in conjunction cases and society development, ecology, environment cleanliness connected with wellbeing, safety and protection of animals, specifically the ones living in the wild. On that account, in the present investigation the attention was drawn to the necessary participation of veterinary sciences in the research on causes and recommendations of decreasing the percentage of iatrogenic multiple pregnancies. These problems as individual and selective issues are not sufficiently examined and need further investigations.