The rate reached a 12-year low in 2009, when there were about 102 pregnancies for every 1,000 women aged 15 to 44, according to the latest statistics from the U.S. Centers for Disease Control and Prevention.
That rate is 12 percent below the 1990 rate of about 116 pregnancies per 1,000 women. Only the 1997 rate of 102 has been lower during the past 30 years, according to the report.
Experts said two factors are driving the downward trend: improved access to birth control and decisions by women to put off childbearing until later in life.
Those trends have caused the average age of pregnancy to shift upward.
Pregnancy rates for teenagers also have reached historic lows that extend across all racial and ethnic groups. Between 1990 and 2009, the pregnancy rate fell 51 percent for white and black teenagers, and 40 percent for Hispanic teenagers.
The teen birth rate dropped 39 percent between 1991 and 2009, and the teen abortion rate decreased by half during the same period.
Overall, pregnancy rates have continued to decline for women younger than 30.
"The amount of knowledge that young women have about their birth control options is very different compared to a few decades ago," said Dr. Margaret Appleton, director of the division of obstetrics and gynecology at the Scott & White Clinic in College Station, Texas. "Birth control is more readily available to women, and they are more knowledgeable about it."
Image: Pregnant woman, via Shutterstock