I think that the previous thoughts about where you stand on the issue or upon which side your writing will be focused is vitally important in determining how this paper will progress. Equally important will be ensuring that you follow your task rubric or description in the requirements of the paper. I think being able to formulate how the paper will look essential. Do you need to present a persuasive case as to both sides of the issue, with judgment at the end? Do you need to explain anything about why the issue is so intensely debated on either side? Is the paper straight explanation of your opinion? What kind of facts are needed in terms of what has to be shown? These are topics that need to be explored before writing and pondering or reflecting about them might help in the writing process and composition of this writing sample.
Does your essay have to take a position on the issue, or are you just presenting facts? You are not really clear.
I am opposed to elective abortion, so I will offer you some pre-writing thesis ideas based on my personal viewpoints on the issue. Others that are pro-abortion can offer some opposing ideas and then you can choose which one you think you would like to write about. I have volunteered with women in a crisis pregnancy center and I have learned through my experience that there is a lot of guilt associated with abortions. Young women do not think about this when they first come in -- they just want the abortion -- but those that do choose to have an abortion don't just breezily walk away afterwards. Sometimes the guilt lasts a lifetime.
Many young women choose abortion because they think it is a quick fix for a difficult situation. One survey indicated that of women who have had abortions, 63% felt "forced" into it by others -- either a family member, the father, medical personnel, parenting organizations, etc. In this same survey, 74% of the women said they would not have the abortion again, but would choose other options, such as adoption or keeping the baby. Religious reasons aside, this is a very painful decision for a young woman and to tell women that it is "a simple medical procedure" is a half-truth that totally ignores the emotions of women.
So, some thesis statements could be:
Terminating a pregnancy often causes guilty feelings that can last a lifetime.
Aborting a baby is not an easy decision.
Aborting a baby takes away the rights of the unborn child.
I know this is a controversial topic and many people will not agree with my views, but you have to decide what to write for yourself.