I'm pro-choice, but in the sense that I think abortion is a necessary evil. I don't like the idea of killing babies, but I also don't want girls cutting themselves up, drinking poisons, or having someone beat them up and cause serious injuries. Also, in cases of rape, incest, mother's health, I think it should be an option. Further, I don't feel it's really my business to tell another woman whether or not she's ready to have a baby.
However, I also don't like the idea that children are commodities and that we can engineer them to be who we want them to be. Aborting a pregnancy because you're really struggling or because something bad happened to you makes sense because you're choosing between two less than ideal situations. Aborting a twin in a healthy pregnancy, where you're otherwise stable, just because you didn't want to deal with extra work sounds callous to me. What will your kid say if you tell them that? It would make sense if their twin was dying but not if their twin was healthy.
For me, it's the same reason aborting babies with Down's Syndrome makes me uncomfortable (since now, more than ever, they have a chance to live happy, healthy, and fulfilled lives). It's the same reason aborting a baby who happens to be a certain gender makes me uncomfortable. Where do we draw the line? Are we going to abort babies who don't look a certain way (which we may be able to know, with increasing technology)? Who don't possess a certain talent? Are we going to turn into Gattaca, where it was looked down on to conceive naturally, for fear it would be genetically inferior?
Of course, some feminists will say, "If you're pro-choice, you have to be for every choice." I don't necessarily agree with that. We're all at different points and there are ways we draw the line. I am pro-choice because I do think there are situations where abortion may be justified and I don't think mothers or doctors should be arrested. However, I think doctors should have ethical guidelines when it comes to anything fertility related. These are babies and potential babies we're talking about. They are not new pairs of shoes, shades of lipstick, or cute handbags. It's one thing to want to plan your family responsibly and to have to make a difficult choice, because of your finances, health, or any other children you may have. It's quite another to decide that you can't love a particular child because it will interfere with your lifestyle somehow. Parenting is hard work, whether single babies or twins, special needs or not (barring ones where pregnancy could pose a huge threat to both mom and baby), boys or girls. If you're not up to it for one, you're not up to it at all.