At conception, God entrusts the couple with a soul, which will reside within the child to be born. The baby is accompanied by a spiritual image that corresponds to an image in the upper world. Before a person’s death, that spiritual image departs, and this is a sign that he is about to die:

At the moment when a man undertakes to sanctify himself and engage in intercourse with his wife with his holy will, a holy spirit awakens in him, which includes [both] male and female elements, and the Holy One, blessed be He summons the messenger who is appointed over human pregnancies, and deposits with him that spirit, and tells him where to deposit it…The Holy One, blessed be He, infuses into that spirit everything that He infuses, and [the Sages of the mystical Torah] have explained this.

A person is accompanied by a spiritual image in this world, and parallel to this there is an image in the World to Come:

Then a spirit descends, and an image is with it, that which corresponds to its form above. He is created in that image and he walks in this world in that image. This is as it is written: “Surely man walks with an image” (Psalms 39:7). While this image is with the person, he exists with it in this world and in the next world, and the two of them are joined together as one.

Before a person dies his image departs from him:

When a person’s time for leaving this world approaches, the evil spirit [that is a result of contact with the physical world] that had clung each day to the elevated image that was given to him comes and takes the image and uses it to rectify itself, and [the elevated image is repaired and] departs, and never again returns to that person. Then one knows that he has been turned away from everything [and is about to die]. (Zohar 3:43a)

Further reading: For more on pregnancy and birth, see A Concise Guide to the Sages, p. 407; A Concise Guide to Halakha, p. 3.