A map shows birth rates in America by state, from 2007 to 2009. National Center for Health Statistics hide caption toggle caption National Center for Health Statistics The Two-Way U.S. Birth Rate Drops; Recession Or Abstinence? March 31, 2011 The U.S. birth rate fell 4 percent between 2007 and 2009 — more than any two-year span in 30 years. Some researchers blame the decline on the recession. But a separate study finds that abstinence, and possibly online porn, may also play a role.