Could we consider then, that the birth of a soul is at a different time as the birth of the physical body, meaning it isn’t at conception, nor at the embryonic stage and not even upon delivery? A newly born baby would have a mental capacity and capability that are less than a grown-up animal so if we consider an animal as not having a soul, how could a baby have one then? Using this measurement, ie mental capability, could I venture that a soul would get born once a baby human reaches a particular point in his or her life where his/her mental capacity reaches a level where he/she is distinctly different from an animal? This birthdate would then be different from persons to persons, solely depending on the development of the brain, and once that threshold level is reached, an immortal soul would be born and lives on from that time onwards, even after physical death. We probably will never know or understand when this threshold level can be reached to result in the birth of a soul, but I think this is not as problematic as determining the timing of the soul between conception and birth. Of course, this is just speculation on my part, but I think it is still a possibility. Otherwise, there would be a lot of soul-less souls (ie souls without personality or character) resulting from the many miscarriages, abortions, still births, frozen embryos outside the wombs, and even microscopic foetuses of a few days old that didn’t get attached to the uterus successfully.
I think we can liken this to the sudden appearance of a flame in a piece of hot charcoal. A piece of charcoal can be red hot but yet not hot enough to produce a flame. However, continuous fanning of the hot charcoal will eventually cause a flame to be ignited suddenly when it reaches a certain temperature. This is exactly what I envision of a soul suddenly bursting into life in a baby when a certain level of personality, character, consciousness and many other mental levels or maturities are reached. The soul would have to exist beyond the 3 dimensions of space we live in, and who knows if it could be the driver of the brain in the 4th dimension?