Women undergoing certain infertility treatments are more likely to become pregnant if they take part in a simultaneous stress reduction program, new research shows.

The finding, published in the journal Fertility and Sterility, raises new and controversial questions about the role that stress may play in infertility.

The issue is a delicate one because historically, doctors often laid the blame for a couple’s inability to conceive on psychological and emotional issues in one or both partners. But research shows that most infertility is the result of physical problems in a man’s or woman’s reproductive system, and psychological factors are rarely the primary cause.

“It’s an extremely sensitive topic for couples,’’ said Alice D. Domar, a psychologist at Beth Israel Deaconess Medical Center in Boston and director of mind-body services at Boston IVF, a large fertility center. “The most common, unwelcome piece of advice to couples is ‘just relax and you’ll get pregnant.’ ”

Even so, a diagnosis of infertility can cause considerable stress and sadness, and patients often report high levels of depression and anxiety. Some studies have compared the stress of infertility to that experienced by patients with cancer or heart disease.

To assess the effects of high levels of stress, researchers are studying whether stress may make the body a less hospitable place for a pregnancy and somehow interfere with the success of fertility treatments. Many large infertility programs offer individual and couples counseling to help men and women cope with the diagnosis and treatment, but it’s not known if any particular type or duration of treatment may affect success rates.

To find out, Dr. Domar and colleagues recruited 100 Boston women under 40 who were taking part in in vitro fertilization, or I.V.F., in which embryos formed in test tubes are implanted in a woman’s body to help her become pregnant.

The women were randomized to a control group that received only the fertility treatment or a group that received fertility treatment as well as a 10-week stress management program that focused on cognitive behavioral therapy, relaxation training and social support.

Researchers tracked the groups through two I.V.F. cycles. In the first cycle, there were no differences in conception rates between the groups. Dr. Domar said that only about half of the women in the mind-body treatment group had begun the program, and those who had started had completed only a few sessions.

In the second cycle, most of the patients had attended at least five mind-body sessions. At that point, 52 percent of the women participating in the stress reduction program had become pregnant, compared with 20 percent in the control group.

“It’s not that it’s all in your mind,’’ Dr. Domar said. “If you’re really stressed out and depressed, the body seems to sense that’s not a good time to get pregnant. There’s something about practicing relaxation techniques or being with other women who understand what you’re going through, probably a combination of everything, that makes a difference. It isn’t just about relaxing.”

The mind-body program includes an exercise called “cognitive restructuring,” in which women are asked to share recurring negative thoughts. Common thoughts include “I’m never going to be happy unless I have a baby,’’ or “It’s my fault for waiting too long.”

Through a series of exercises, the patients are taught to replace the negative feeling with a more positive but still realistic thought — for example, “I’m doing everything I can to have a healthy baby.’’

“For a lot of patients, cognitive restructuring is a huge breakthrough,’’ said Dr. Domar. “Helping them tap into the hope they have is a really powerful thing, and you wouldn’t do an I.V.F. cycle unless part of you believed it would work.’’