More US women using the 'morning after' pill: report

That trend may reflect increased wariness among Americans to have children amid the 2007-2009 economic recession, the effects of which are still being felt by many, according to researchers at the Guttmacher Institute, which also tracks birth control use.

"At the same time, it can make it harder for people to have access to birth control because of costs," especially for disadvantaged women who face higher rates of unintended pregnancies, said Lawrence Finer, head of domestic research for the reproductive research group.

That situation could change in the wake of the 2010 healthcare overhaul that required health insurers to begin covering birth control last year, although the law faces legal challenges.

Religious groups, particularly Catholics, charge that the provision violates their belief against artificial birth control and are fighting to block it.