Wikipedia
In religion, ensoulment is the moment at which a human being gains a soul. Some religions say that a soul is newly created within a developing child and others, especially in religions that believe in reincarnation, that the soul is pre-existing and added at a particular stage of development.
In the time of Aristotle, it was widely believed that the human soul entered the forming body at 40 days (male embryos) or 90 days (female embryos), and quickening was an indication of the presence of a soul. Other religious views are that ensoulment happens at the moment of conception; or when the child takes the first breath after being born; at the formation of the nervous system and brain; at the first brain activity; or when the fetus is able to survive independently of the uterus ( viability).
The concept is closely related to debates on the morality of abortion as well as the morality of contraception. Religious beliefs that human life has an innate sacredness to it have motivated many statements by spiritual leaders of various traditions over the years. However, the three matters are not exactly parallel, given that various figures have argued that some kind of life without a soul, in various contexts, still has a moral worth that must be considered.