I found this interesting

Article about unintended pregnancies in marriage, and complaining about how the government programs are designed primarily to reduce the number of out of wedlock pregnancies and births but do not address the problem of unintentional pregnancies in marriage. I thought it was interesting. Though they seemed to neglect to consider the possibility that many unintended pregnancies in marriage are not reported as such, which seems like it should be an important thing to consider when asking the question why married couples have fewer unintended pregnancies than unmarried couples even though they have more sex.

http://www.agi-usa.org/pubs/tgr/06/2/gr060210.html