WASHINGTON — The U.S. abortion rate dropped during the 1990s, according to a report by the Centers for Disease Control and Prevention (CDC), a federal agency. Between 1990 and 1999, abortions among adult women dropped from a rate of 27.4 abortions for every 1,000 women to 21.4 abortions, according to the report. The decrease represents a 22 percent decline. Among…