There are two moving parts to the debate. One part, a woman's right to her body is the only relevant issue at stake.
But the other angle by which one could approach the debate is to claim: "an infant is a person with rights." This is generally the chief concern of pro-lifers. But even some pro-choicers are interested in this part of the debate. What makes a fetus a person? If a fetus is a person, when (along the course of its development) does it attain "personhood"? Plenty of pro-choicers have given thought to the matter and made determinations.
For example, the fertilization of the egg cell cannot be a genuine marker for personhood mainly due to something called "cell potency." Post conception the fertilized egg divides into cells which are totipotent. This means that you could theoretically divide these cells into three groups and grow each one in a separate test tube. The result would be three different persons if you did this. So, according to this line of thinking, personhood absolutely cannot begin at fertilization.
I'm personally interested in both angles of the debate. Or, at the very least, I find OP's approach refreshing, because it's different from what we usually hear.