(HealthDay) -- More than a third of births in the United States stem from unintended pregnancies, a number that's remained steady in the United States from 1982 to 2010, a new government report indicates.
The make-up of women having these births, however, has shifted over time from white to Hispanic and to those in their teens and 20s, according to the U.S. Centers for Disease Control and Prevention.
"We have made no progress since 1982 in reducing the percentage of births that are unintended," said report author William Mosher, a statistician at CDC's National Center for Health Statistics. "It was 37 percent in 1982, and it's still 37 percent."
The report was released Tuesday.
"Intended" births are planned, Mosher said. "Unintended" births are those that are either "mistimed," which means they occur either a short time or years before the mother had planned to become pregnant or "unwanted," which means a mother did not want the pregnancy, whether or not she already had other children.
For example, in 2008, of the roughly 4.2 million births, 1.6 million were unintended, 600,000 were unwanted, another 600,000 were mistimed by more than two years and 400,000 were mistimed by less than two years, according to Mosher.
"There was only one group where we made some progress and that is among white married women," Mosher said. "But, they account for a smaller and smaller proportion of the births."
In 1982, white women accounted for 66 percent of all births. In 2006-2010 they accounted for 43 percent, Mosher noted.
"More unmarried women and more particularly more Hispanic women account for more of the births these days than 30 years ago," he said.
"The ability to have births when you want them varies across the population," Mosher said.
Women who have mistimed births of less than two years are more likely to be better educated and married than those whose birth is mistimed by more than two years, Mosher said.
In 2002, 86 percent of intended births were to women with college educations, compared with 58 percent to women with less than a high school education, according to the report.
Moreover, women who have unintended births tend to be poorer, Mosher said. According to the report, 35 percent of intended births were paid for by Medicaid, compared with 65 percent of unintended births.
And Medicaid paid for 75 percent of births for women who had births more than two years before they intended. "That's an indicator that she wasn't ready," Mosher said. "She wanted to finish high school, college, job training or get married before she had a baby."
Unintended births are costly. Mosher noted that medical care for unintended pregnancy costs $11 billion a year, much of which are Medicaid dollars.
The new report "shines yet another light on the fact that low-income and underserved women are significantly more likely to experience unintended pregnancies, which can have detrimental consequences for women and their families," said Deborah Nucatola, senior director of medical services at Planned Parenthood Federation of America. "Full implementation of the Affordable Care Act's Medicaid expansion efforts and the women's preventive health provision -- which in August will begin requiring private insurance plans to cover birth control without co-pays -- will be crucial steps towards guaranteeing that all women, regardless of income, have access to effective birth control."
Major differences also exist in intended and unintended births by age, Mosher said.
"For teenage mothers, 23 percent of their births are intended -- that means that 77 percent are not," he said. "If teens had only the births they intend we would have one of the lowest teen birth rates in the world -- we don't," he said.
For women aged 20 to 24, only half of their births are intended, Mosher added. "It's not until 25 and older that three-fourths of births are intended," he said.
There are also striking differences in intended and unintended births based on marriage, Mosher said.
For example, 77 percent of births to married women are intended, 49 percent of births to unmarried women living with a partner are intended, but only 33 percent of births to single women without partners are intended, he said.
"A lot of us who are parents think parenthood is just a delight for everybody, and that's certainly not what this report suggests," Mosher said.
Unintended births are both a public health and social problem, he said.
"If all births in the U.S. were intended there would be very few teen births, there would be much fewer births to unmarried women, there would be much fewer births to 20- to 24-year-olds," Mosher said. "Parenthood would be concentrated to married and cohabiting women 25 to about 39."
More information: For more statistics on U.S. births, visit the U.S. Centers for Disease Control and Prevention.