I hope I'm not too late, but I'd like to submit my reasoning for when life begins and open it to criticism.

If I get into an accident and become completely and irreversibly brain-dead (not a coma but brain-dead) and machines have the ability to keep the rest of my body permanently alive (they're not quite there yet but let's pretend), then most of my body exists but my mind does not exist. Yet my family would personally consider me to be dead and would have the right to pull the plug. This is because, regardless of my body's state, I am no longer mentally alive and lack a mind. So if not being mentally alive is a threshold for losing personhood status, it should be a threshold for gaining personhood status as well. Until I have a mind I should not be considered alive.

Another analogy is if I magically had the power to upload my mind to the internet, and then my human body was suddenly destroyed. As long as my mind exists in some way, I'm still considered alive, even if my body no longer exists. So if I have a body but no mind I'm dead, and if I have a mind but no body I'm alive. So what makes a person a person is not a body but a mind.

Personhood can begin at two stages. It can begin at conception when the body begins, or it can begin at consciousness when the mind begins. Given the analogies it just makes sense for it to begin at the latter. The human fetus does not gain the capacity to think and feel until 24-28 weeks, and 99% of abortions in the US occur before 20 weeks.

Another counterpoint against life beginning at conception is that 30-50% of all pregnancies end in a miscarriage (Only 10-20% of noticed pregnancies, but for total fertilized eggs it's 30-50%). If your pro-life stance is religiously rooted it wouldn't make sense for God to make the human body so that nearly half of human souls end before their born.

Shakier ground: Also while being the ability to think and feel is there at 24 weeks, the human fetus is still in a state of complete unconsciousness, and hasn't thought their first thought yet, and probably won't until birth. It could be argued they still have passed the moment of true consciousness yet. Combined with the whole women's rights argument, it may be doable to allow the choice for abortion for the rest of the pregnancy as well.