The abortion rate fell between 2000 and 2008 for most groups of women except one, poor women, according to a new analysis released Monday.

The overall abortion rate declined 8 percent between 2000 and 2008, dropping from 21.3 abortions per 1,000 women to 19.6, according to the analysis by Rachel Jones and Megan Kavanaugh of the Guttmacher Institute, a private nonprofit reproductive health research group that provides some of the most authoritative data about abortion in the United States.

That reflected a drop in the abortion rate for most groups of women except poor women, who accounted for 42 percent of all abortions in 2008. Among poor women, the abortion rate increased 17.5 percent, rising from 44.4 to 52.2 per 1,000 women, according to the analysis, which is being published published in the June issue of the journal Obstetrics & Gynecology.

The study did not examine the reasons for the trends. But the researchers speculated that the recession may have played a role.

“The economic recession that was occurring in 2008 may have made it harder for poor women to access contraceptive services, resulting in more unintended pregnancies,” the researchers wrote.

“Alternately, when confronted with an unintended pregnancy, poor women who might have felt equipped to support a child, or another child, when not in the midst of a recession may have decided that they were unable to do so during a time of economic turmoil, ” they wrote.

The analysis was based on data collected by the Guttmacher Institute’s 2008 Abortion Patient Survey, Census Bureau Current Population Surveys conducted in 2008 and 2009, and the federal government’s National Survey of Family Growth conducted between 2006 and 2008.

The abortion rate decreased 18 percent among African American women during this period, which represents the largest decline among the four racial and ethnic groups examined.

Based on the overall abortion rate, the researchers estimate that nearly one out of 10 U.S. women of reproductive age will have an abortion by age 20, one quarter will have an abortion by age 30 and nearly one-third will undergo the procedure by age 45. But the proportion of women who have an abortion in their lifetime has been declining. It fell from 43 percent in 1992 to 30 percent in 2008 as the overall abortion rate declined.

Here’s a link to a new video the Guttmacher Institute put together on abortion in the United States.