Women do not put their mental health at risk by having an abortion, according to an authoritative study that will undermine the campaign to tighten the UK's abortion laws.

A comprehensive review of research by the American Psychological Association (APA), one of the world's most influential mental health bodies, found no evidence that the majority of abortions cause psychiatric problems.

By challenging a key scientific argument for reform, the findings will hinder the latest effort to make it harder for British women to obtain terminations, which is to be debated by the House of Commons in October.

Anti-abortion MPs have tabled an amendment to the Human Fertilisation and Embryology Bill that would require all women to be counselled about psychiatric risks before they can be cleared to have a termination. They cite research suggesting that mental health issues such as depression and anxiety are more common among women who have had abortions.

The APA report said that the findings of such studies were unreliable because they either failed to distinguish between abortions of wanted and unwanted pregnancies, or they did not consider factors such as poverty and drug use that raise the likelihood both of having an abortion and suffering mental illness.

The APA found “no credible evidence” that single abortions could directly cause mental health problems among adults with unwanted pregnancies. It called for more well-designed studies to investigate the issue.

Even the evidence for adverse psychiatric effects of multiple abortions was equivocal, it found. Higher rates of mental illness among such women could be explained by social factors, such as poverty or drug use that also put them at higher risk of unplanned and unwanted pregnancy.

Brenda Major, who chaired the task force, said: “The best scientific evidence published indicates that among adult women who have an unplanned pregnancy the relative risk of mental health problems is no greater if they have a single elective first-trimester abortion or deliver that pregnancy.

“The evidence regarding the relative mental health risks associated with multiple abortions is more uncertain.”

The report, which was published last week at the APA's annual conference in Boston, found evidence that women who had late abortions because of foetal abnormalities often suffered adverse psychological reactions, similar to those experienced by women who had miscarried or had a stillbirth. These effects, however, were seen among women who had lost a wanted pregnancy, and should not be extrapolated to those who chose to terminate for other reasons. They were also less serious than those seen in women who gave birth to infants with life-threatening defects.