Check out this ABC story about a recent survey of women who had abortions in Minnesota in 2007. A record number of them, 40%, cited economic reasons, such as being unable to afford another child, as a motivation for abortion.
The overall number of abortions was down, however. This matches the general trend of the last few decades, minus a statistical blip in 2006.
It is probably wrong to say that the worsening economy has caused more abortions. Women who have abortions do so for very complicated reasons that are often hard to articulate to pollsters. The more likely explanation is that more women, when asked to justify their abortion to a strange person with a clipboard, latch on to economic concerns as a publicly acceptable reason, because the economy has been in the news so much recently.
Catherine Price at Salon agrees that women may be citing economics to justify a decision they feel guilty about. But she also points out that all the factors women cite in having an abortion--"not wanting to have children at this time, already being a single parent and unfulfilled educational goals"--are tied to economics. She also has some funny things to say about the strange graphic ABC chose to include with the story.