I doubt there has been a study but I would be interested to see it if it had as well.
Anyway, I would be completely shocked if it turned out that the large majority of abortions are not liberal.
You do understand that most conservatives believe abortion is murder right? I would have a tough time thinking many girls would do something they believe to be murder.
Of course I understand that most conservatives look on abortion with disfavor. However, under certain circumstances, some people will act against their principles. Perhaps, under certain economic conditions or at the demands of a partner, someone may make a choice to get an abortion.
Going with my gut, I would tend to feel that the majority of those who decide to get an abortion are liberal. However, not seeing any sort of data or study on the self-identified political ideologies of people who get an abortion, I make this statement with no certainty and it is, for all effects, meaningless, as are your similar statements. Very well the majority of women who get abortions could be self-identified liberals, or maybe it's close to half and half, or, maybe even, a good number of these women are politically apathetic or don't identify with any political ideology. The thing is, we don't know.
These women who have made the choice to get an abortion have made a very difficult decision. We likely do not fully understand the circumstances involved that motivated them to make such a decision. Rather than reducing the issue of abortion to the typical conservative-liberal slap fest, we should make an effort to understand what situations and circumstances lead to a woman making such a choice (such as things, perhaps, like access to and cost of contraception), so as to deal with such circumstances in the hopes of more women not being put into the situation where they even have to make such a choice (taking that choice away, however; doesn't address such problems). As they have made a very difficult decision, whether we agree with it or not, I think these women deserve to not be berated by individuals attempting to take the moral high ground, or to be called murderers, or to have their difficult decision reduced to a means by which to make little quips about political ideologies we don't like (i.e. "liberals are killing themselves off"). Abortion is, after all, a complex and serious issue that directly affects the lives of many and indirectly affects the lives of all.