Extract from link:

"Donohue and Levitt (2001) presented evidence that the legalization of abortion in the early 1970s played an important role in the crime drop of the 1990s. That paper concluded with a strong out-of-sample prediction regarding the next two decades: “When a steady state is reached roughly twenty years from now, the impact of abortion will be roughly twice as great as the impact felt so far. Our results suggest that all else equal, legalized abortion will account for persistent declines of 1% a year in crime over the next two decades.” "

[law.stanford.edu]

An a critical look at the hypothesis:

[freakonomics.com]