LONDON - Abortion does not increase a woman's chance of developing mental-health problems, according to a British health agency's review of dozens of studies worldwide over 20 years.

Among women with unwanted pregnancies, those who had abortions were no more likely to suffer from problems including anxiety or depression than women who gave birth, the analysis by the United Kingdom's National Collaborating Centre for Mental Health found.

The research offers "reassuring news" that abortion does not cause mental-health problems, but raises a warning that officials must address the problem of unwanted pregnancy, said Tim Kendall, the center's director.

The report is likely to be disputed by those opposed to the practice and believe that terminating a pregnancy can trigger depression or other mental illnesses.

Kendall said mental-health problems seemed to be linked specifically to unwanted pregnancies rather than abortion.

About 11 to 12 percent of women in general suffer from mental-health issues such as anxiety or depression, but among women with unwanted pregnancies, that figure rises to about one-third, he said. For women who later had an abortion, there did not seem to be any further increase in their rate of mental-health problems.

"We should be looking at what it is about the unwanted-pregnancy stage that is so problematic," he said. "We need to try to get those women help sooner so they're not put at greater risk."

Kendall and colleagues reviewed 44 studies from sources including national health systems and insurance databases conducted worldwide from 1990 to 2011 that included several million women with unwanted pregnancies.

They concluded the best predictor of whether women would have a psychiatric problem after an abortion was whether they had mental-health issues before getting pregnant. Kendall said it was possible that women with mental-health problems after an unwanted pregnancy were at greater risk of getting pregnant or that an unwanted pregnancy worsened their mental health.

The review was released Friday by Britain's Academy of Medical Royal Colleges and the Royal College of Psychiatrists. It was paid for by the United Kingdom's department of health.

Kate Guthrie, a spokeswoman for the Royal College of Obstetricians and Gynecologists, said in a statement it was key that health-care staff provide follow-up care to women vulnerable to mental-health problems after they terminated their pregnancy. She was not connected to the review.