The rate of unintended pregnancy in the United States has declined to its lowest level in the last three decades.

The level in 2008 was 54 per 1,000 women and girls aged 15 to 44. By 2011, it was 45 per 1,000. Of the 6.1 million pregnancies in 2011, 2.8 million were unintended.

A recent analysis in The New England Journal of Medicine found variations in rates of unintended pregnancy by income, race, ethnicity, education and age. But there were declines, some quite large, in almost every demographic group.

The rate among teenagers, for example, declined by 28 percent. The rate of all income groups dropped, with the largest decrease — 32 percent — among people with incomes at 100 percent to 199 percent of the poverty level.