"Many Americans will welcome the news that there are fewer abortions, particularly among teens, and that a larger proportion of abortions are now happening very early in pregnancy," said Sharon Camp, president of the Guttmacher Institute which compiled the report.
The teen abortion rate fell by more than half, from 42 abortions per 1,000 teenage girls in 1989 to 20 per 1,000 in 2004, said the report, which looked at trends among women who had abortions in a 30-year period starting in 1974 -- a year after the Supreme Court legalized abortion in the United States.
The rate for all women aged 15-44 was 20 abortions per 1,000 women in 2004.
Overall rates of abortion in the United States peaked soon after the procedure was legalized in 1973, remained fairly constant through the 1980s, and have declined steadily since then, according to the report.
"After reaching a peak of 1.61 million in 1990, the number of abortions declined to about 1.22 million in 2004, even as the population of the country continued to grow," the report said.
From 1974 to 1989, 18- to 19-year-olds had the highest rate of abortion among all women, peaking during those 15 years at 62 abortions per 1,000 women in their age group, the report showed.
But teen abortions have been declining steadily since.
"A large part of the decline in abortion among teens -- which began long before abstinence-only sex education programs began receiving federal funding -- is attributable to increased use of contraceptives and use of more effective methods," the report said.
Although abortion rates have fallen across the board for all racial and ethnic groups, Hispanic and black women have disproportionately more abortions than non-Hispanic white women, the report showed.
The rate among Hispanic women was still at 28 abortions per 1,000 women in 2004, and among black women it was more than double the across-the-board rate, running at 50 per 1,000.
The high rates among black and Hispanic women "in large part reflect the increasing size of the minority population in the United States," the report said.