Globally, the proportion is surprisingly consistent: 22 percent in developed countries and just over 21 percent in developing ones. More than one in five human births, based on survey results, are the result of a pregnancy that the woman did not want to happen.
"Based on survey data, approximately 40 percent of pregnancies are unintended in developing countries, and 47 percent in developed ones."
Robert Engelman, "Methods Section for ;An End to Population Growth: Why Family Planning Is Key to a Sustainable Future'" Solutions, Vol 3, No. 2, April 2011, http://www.thesolutionsjournal.com/node/921