Do you believe that a soul is imparted at conception?
Or do you believe it is at birth?
Do you believe the Holy Spirit can be imparted in the womb?
The question is about a
mystery. Something we are not told clearly in scripture (that exact
when in time, though we do seem to know it's before birth sometime it seems from some scriptures, such as when Mary visits Elizabeth, who is well along in pregnancy, and in her womb the baby to be named John (later) leaps in response).
So, all answers that give a guess about just when (any exact moment) are, well, guessing. (Unless the person somehow has scripture to back up a precise time.)
So, in the normal on CF way of guessing about mysteries --
Here's some thoughts about how to guess (which may or may not help).
"...more than half of successful fertilisations will end in miscarriage."
New Research Shows Most Human Pregnancies End in Miscarriage
God would not put souls into fetuses that He can see are going to naturally die before birth, is my best guess.
(if someone believes God would intentionally put a soul into a developing fetus He can see is going to die soon in the womb...I wonder how they see that, and what makes them think so?)
Another aspect to consider: the soul seems to be interwoven with consciousness.
So, if only 1/2 of conceptions result in viable babies that make it full term.
And the soul is associated to consciousness.
Then, it must be very likely that a soul would only be implanted into developing babies that are going to make it and when their developing nervous systems are sufficiently developed in order to allow a basic consciousness.
One possible indicator of basic consciousness is that sometime in the 2nd trimester they do begin to respond --
Fetal Sense of Hearing Development During Pregnancy | What To Expect
So....not before then, but quite possibly at that time, or...
Another interesting fact is that long time Jewish custom was not to name a baby boy until it reached 8 days living outside the womb (during the 'bris' ceremony). And a baby girl during first Torah reading -
The Laws of Jewish Names - Parshat Shemot