Hinduism believes that all souls are connected to other souls via an extensive and complicated system of karma (actions), vasana (wishes) and runa (debt). Firstly, the soul should have the correct runaubandh (karmic debt bonds) with the male and female (of any species) that are about to mate to create a body for the souls to be born. The soul should be prepared to be born emotionally. If the soul is not ready at the time the male and female have sexual intercourse, no life will enter the sperm and egg. For the soul to be born in a new individual, it should have enough karmas to use in this world. Many fertilized eggs never grow into a baby or live to the complete term, as their karmic bonds only last for a short period. In Hinduism, miscarriage happens when the karmic relationship between the soul and the body ends and the soul moves apart of the body before the baby comes to the world.
