Multiples Multiply

The number of twins born in the United States has jumped sharply over the last three decades, according to a recent report from the National Center for Health Statistics. In 2009, an unprecedented 1 out of every 30 babies born was a twin, up from 1 in 53 in 1980.  The rate of twinning rose an average of 2 percent per year through 2004 before leveling ou…