Again, since the person has the right to still have an abortion it isnt a measure of who is more valuable. It is a measure that both have value (without measruing who has more) and ensuring both have their value honored by looking after the bodily autonomy of each of them.
I picked a scenario where both can survive, have their will respected, and the woman still has the right to not follow through with an unwanted pregnancy...
I am far more concerned that you are trying to find the value of two humans so you can determine which has the right to murder the other. I prefer a stance where no murder occurs and both have value.