In the exoteric scripture The Sutra of Conception and the Dzogchen tantras, Buddha Sakyamuni elucidated the process of human conception. After taking rebirth, consciousness enters the zygote and a life is formed, but not yet with a physical body. First, the cleavage of the zygote begins about one week after the conception and then combine again. A few days after combining, the cell division begins again, and the process repeats itself. The shape of the embryo after each division is clearly described in the scriptures, which completely matches that of modern medicine.
It is said in the scripture that, in the intermediate state, beings don’t really know they are going to take rebirth, nor do they know what lies in store for them or how to take rebirth. It goes on to elaborate further: In general, if the intermediate being is going to be reborn in the hell realm, it will feel like going into a dark tunnel or on a dark road; if it is to be reborn in the human realm, it will feel like entering a park or a beautiful palace, so on and so forth.
Depicted from THE HANDBOOK FOR LIFE'S JOURNEY