What is known about the specific time the spirit enters the fetus and then becomes a living child? Much hullabaloo is made over this question with the pro-life crowd and the abortionists. If we could know for certain when the fetus becomes alive with the spirit, perhaps a better decision can be made for adoption rather than for abortion.
From Ask Gramps, Maasai, Inc. Provo, Utah, p. 75:
“The exact time that the pre-mortal spirit enters the mortal body is not specified in divine revelation (See Encyclopedia of Mormonism, Vol.1, BIRTH). Since it is not recorded, it may not be at the same time for every person. However, there is no doubt that the Savior appeared to the Nephites as a pre-mortal spirit on the day before his birth in Bethlehem. Thus, the life of the babe in Mary’s womb was sustained during that time by the life of the mother. Whether the spirit of the Savior was resident in the womb prior to his advent to the Nephites is not recorded.
Although the spirit may enter the body at some indeterminate time prior to birth, there is a time prior to that when the fetus sustains life as part of the mother. At some given time, the spirit enters the body, giving it independent life. It would then be considered a mortal soul. Elder Bruce R. McConkie has touched on this subject in some of his writings. In Doctrinal New Testament Commentary, Vol. 1, p.84, he writes
Luke 1:41. The babe leaped in her womb In this miraculous event the pattern is seen which a spirit follows in passing from his pre-existent first estate into mortality. The spirit enters the body at the time of quickening, months prior to the actual normal birth. The value and comfort attending a knowledge of this eternal truth is seen in connection with stillborn children. Since the spirit entered the body before birth, stillborn children will be resurrected and righteous parents shall enjoy their association in immortal glory. (Mormon Doctrine, pp. 693-694.)
There are many unanswerable questions related to the details of the spirit world and its interface with mortality. As we try to fill in the gaps between the revealed word and our observations we must be careful to draw no conclusions that would contradict any revealed knowledge. Sometimes there is just not enough information available to answer all the questions that could come into our minds. But when we cross to the other side of the veil, where we will be able to perceive both the spirit world and mortality, I imagine that many things that are now mysterious will become obvious.”