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A majority of registered voters across 12 swing states for the first time backs President Obama over likely GOP presidential nominee Mitt Romney for the November election, according to a new USA Today/Gallup poll.

Obama leads Romney by a 51 to 42 percent margin, the poll found. In February, the president trailed Romney in the swing state match-up, 46 to 48 percent. The poll's margin of error is plus or minus 4 points.

The shifting tide of support in Obama's favor was driven by women under 50, fewer than half of whom supported the president in a February USA Today/Gallup poll but swung significantly the other way last month.

More than 60 percent of women under 50 said they prefer Obama, according to the poll. Romney nets just 30 percent support, down 14 points from a month earlier.

Among women overall, Obama holds an 18-point lead over Romney. The former governor carries men by a single point.

Democrats have traditionally held an edge among women voters, with Democratic presidential candidates carrying the key demographic by more than 10 points in the last few general elections. But the gender gap appears for now to be greater than it was during the 2008 election, when Obama won women voters by 12 points over Sen. John McCain.

The USA Today/Gallup swing state survey, conducted March 20-26, covered Colorado, Florida, Iowa, Michigan, Nevada, New Hampshire, New Mexico, North Carolina, Ohio, Pennsylvania, Virginia and Wisconsin.