The pro-life versus pro-choice debate hinges upon our understanding of rights. Here the question is posed in the context of sentience - that is, as beings that suffer pleasure and pain. Putting it thusly suggests a Utilitarian bend. Utilitarianism is a normative ethical theory that argues that there is no higher moral value than that of human happiness, which is defined in terms of pleasure or pain. Hence, it is a hedonic (hedonism is a derived from the Greek word ηδονή which means pleasure) theory. So an action is right when it increases the greatest amount of happiness for the greatest number of beings affected by the action. Each and every sensient being counts for one, or put differently, the pleasure or pain of any feeling being is no more or less morally important important than anyone else's. For all sensient beings "have the same and equal interest to avoid suffering". When considering one's actions one must therefore give equal consideration to the hedonic impact it has on each sensient being and practise that which will increase the greatest amount of pleasure overall.
As far as the issue of abortion is concerned then, an unborn baby would be given equal consideration iff (if and only if) it is considered to be a sensient being, namely a being that can suffer pleasure and pain. Most argue that this occurs once the neurological system is developed.
This is, of course, a matter of personal opinion. There is no way to answer this question objectively. To many people on the pro-life side of the issue, the senses of the fetus would not enter into the debate. To them, life begins at conception, long before there is a fetus that can have any senses. However, I would argue that the senses of the fetus should play a major role in this debate.
In my view, the main question regarding abortion is the question of when the fetus becomes a human being. It is clearly wrong to kill an innocent human being. If I could know with certainty when a fetus becomes human, I would know when (in my opinion) abortion should stop being legal in any given pregnancy. The issue of the fetus’s senses would have a great deal of impact on my thinking about when the fetus is human. The more that the fetus has senses that are akin to those of a baby that has been born, the more I would be opposed to allowing abortion.
The issue of what rights a fetus has is also a matter of opinion. My opinion is that a fetus gains more rights as it gets closer to the full term of the pregnancy. I cannot say exactly what rights a fetus has at each point in a pregnancy, in part because I cannot say exactly how human the fetus is at each moment. To me, the answer goes along a continuum. I would say that a newly fertilized egg has essentially no rights and that (for example) the “morning-after pill” should therefore be legal without restrictions. I would say that a fetus that has been developing for 9 months is essentially human and has all the rights of a newborn infant. In between those times, things are much less clear to me. All I can say for sure is that the fetus has more rights (in my opinion) the longer it develops inside the womb. Again, this is purely a matter of opinion.