Via Matt Yglesias, this New York Times article on anti-choice Democrats shows that while Democrats seem to be making gains in a lot of traditionally conservative places (the article's key example is Bob Casey as an anti-choice Democrat from Pennsylvania), they tend to be electing very socially conservative people to those positions.
The article noted that the nation is "divided" on the issue of abortion, showing Americans roughly split between identifying as "pro-life" and "pro-choice." The piece I wrote recently on pro-choice Republicans shows that this ultimately comes down to branding. The pro-life movement has a done a good job of promoting "a culture of life" and "choosing life," but their framework fundamentally hinges on a pro-choice stance -- that women can make a choice not to have an abortion. Many people might identify as "pro-life" because they don't like abortions. They're icky. They wouldn't have one. But the answer to the question of whether or not abortion should be legal changes those proportions slightly. Responses also slant a lot more pro-choice when you ask whether or not the government should have a say over someone's right to abortion.
When you get down to the specifics, it seems that there are a lot of Americans that are uncomfortable with the idea of abortion, but they don't exactly want it to be illegal. The very fact that exceptions like rape and incest (conditions that are very difficult to "prove" to have a timely abortion). The very label "pro-life" could very well mean that you don't think people should have abortions, but they're not really willing to make such a private choice subject to the law.
Now, I'm not exactly sure how the Democrats the Times profiled fall into that paradigm, but what this does say to me about party politics that while Democrats have been willing to take on a strong pro-choice platform, when it comes down to getting more seats in Congress, pro-choice is still negotiable. Obviously both parties want to be "big tents" with differing views on various issues, including choice. But when women's health and autonomy is still considered negotiable that's very disheartening to a lot of pro-choice activists.