NEW YORK (AP) — The nation’s record-low teen birth rate stems from robust declines in nearly every state, but most dramatically in several Mountain States and among Hispanics, according to a new government report.

All states but West Virginia and North Dakota showed significant drops over five years. But the Mountain States of Arizona, Colorado, Idaho, Nevada and Utah saw rates fall by 30 percent or more.

In 22 states, teen Hispanic birth rates plunged at least 40 percent, which was described as “just amazing,” by the report’s lead author, Brady Hamilton of the Centers for Disease Control and Prevention.

What’s driving the declines? No one can say for sure. Experts believe the explanation is complicated and probably varies a bit from state to state. The national figure has been falling since 1991, aside from a brief interruption in 2006 and 2007.

The CDC report released Thursday is based on birth certificates for 2007 through 2011. Last year, the CDC announced the overall improvement in teen births: a record low of 31 births per 1,000 teens ages 15 to 19. That compares with 42 births per 1,000 five years earlier.

The new report focuses on state figures in 2011:

— Lowest rates are in New Hampshire, Massachusetts, Connecticut and Vermont, each with rates under 17 per 1,000.

— Highest rates overall continue to be in the South, led by Arkansas and Mississippi, each with rates of about 50 per 1,000. In Arkansas, the majority of teen births are to white moms. In Mississippi, the majority are black.

— White teens continue to have the lowest birth rate nationally — about 22 births per 1,000. Black teens saw a larger improvement, but their rate was still more than twice the white rate, at 47 per 1,000.

— Overall, the Hispanic rate plummeted from 75 to 49 per 1,000, now virtually a tie with the black rate.

The teen drop in the last five years coincided with an overall decline in births, which experts attribute to a weak economy that dampened enthusiasm for having children.

Hispanic women have been part of that trend, possibly due to the economy and to illegal immigration crackdowns in some states that reduce the number of young Hispanic females entering the country from Mexico and other nations, said John Santelli, a Columbia University professor of population and family health.

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