After seeing Jasson's post last week (below) and now reading this, I am intent on seeing Juno this week, as well as the substantially darker 4 Months. This J. Hoberman article is phenomenal. Even if you loved Knocked Up, as I did, you will recognize the inversion of choice (ie. pro life agenda) when it's called out.
Here is the soul of its thesis:
"There can be no female agency in Knocked Up, Waitress, and Juno—not because they are comedies, but because, in each scenario, unwanted pregnancy is the joke played (by God?) on the female lead. As the most successful of the preg protags, she who is Knocked Up is necessarily the most smacked down—the glass ceiling turns out to be Alison's own uterus. Jenna and Juno are less formidable, but unexpected fertility mocks their dreams of autonomy. All three are taught their place by their own bodies—and what's more, they learn to like it."