You have several problems within your problem statement.

One problem is the unnamed collective. Who are these "liberals"? Do you allow for those who self-identify as "liberal" but who are not pro-choice?

You also link the unborn baby with the expectant mother, an obvious connection. However, they have different interests. Many here would claim that the unborn child can have no interests, not being a rational creature. Even if we grant that the unborn individual has a clear interest in being born, the mother's contrary interest cannot be ignored.

More subtly, and intractably, life is not an absolute value. People commit suicide, and not always out of despair or neurosis. Soldiers receive (posthumous) medals for it if a "greater good" is achieved. "Failure to thrive" may be the infant's choice to die.

If abortion is murder, is a miscarriage manslaughter?

While terminating a pregnancy commits the wrongful act of taking an innocent life, it is easy to argue that that prevents the greater harms and wrongs that are inevitable from an unwanted child. The child will grow up suffering and most likely bring suffering to others.

All of that is to say that so-called "liberals" may be consistent in their desire to have the best outcomes for every case, whether endangered species or endangered human individuals. One determinant that separates so-called "liberals" from so-called "conservatives" is that liberals are open-minded and propositional whereas conservatives seek absolute rules. You can see this in the rhetoric of the free market. "Classical liberals" such as Milton Friedman and F. A. Hayek spoke differently about capitalism than did self-identified "conservatives" William F. Buckley, Jr., and Ernst van den Haag. So,the bottom line may be that for the "liberal" it is not a callous disregard for the life of the unborn infant, as it is a concern for the well-being of the woman who must be free to choose.

Thanks for your comment. I Understand pro choice is not just a liberal claim and a reasonable person could be in the same camp. But the most active in the animal rights group don't seem to have the same concern for the fetus or the expectant mother.
I do respect all living things as long as they don't tread on me.

Having a "pro-choice" position is not the exclusive realm of "liberals". Packaging the two concepts as if they help define each other is inaccurate.

I'm less worried how someone treats chickens or pigs; I am interested in how someone treats real people.

I know that women who have an abortion often times grieve and regret their decision causing them great pain. I have and continue to grieve the loss of my son , and know many other parents who have suffered the death of a child . The pain and sadness is the worst a human will ever feel.
I am not advocating changing the abortion law.
I think more effort should be put forth to communicate and educate about preventing an unwanted pregnancy.
I just don't understand why liberals are so pro choice.