Technically it is alive when it is still an egg, before it is fertilized (sperm on the other hand is not alive). The real question is when does the creature gain 'personhood'.
To answer this question, we must look at what makes a person a person: what separates us from the animals, what makes us valuable? It is not that we have a beating heart, not that we have DNA, nor our state of having 10 fingers; what makes us valuable is our minds. It is the fact that we feel, have dreams, ambitions, can feel empathy, sympathy, yes even rage and guilt and hate. The fact that we can think logically, arrive at conclusions, make decisions... that is what makes us people!
We know that all of these actions come from the frontal lobe of our brain, and a fetus starts having frontal neural activity somewhere in the 21,22 week range. I say that is the best place to declare personhood.