Abortion continues to be a major political, cultural and spiritual battleground, and the question of whether abortion is linked to mental health problems in women has long been a part of this debate.

Assessing the effect of abortion on mental health is complex and controversial, and findings are frequently conflicting. Even though studies may show an association or link between the exposure variable, abortion and a health effect, the way that studies are designed mean that we cannot always be certain that the exposure definitely causes the health effect. It is simply not possible to conduct a randomised controlled trial assigning some women to an abortion group and others to a birth group.

Yet it is essential to do the research. Nearly 200,000 abortions are carried out in Britain each year, so even minor psychological effects on a few women will affect large numbers in total. Moreover, around 98% of abortions are carried out in the UK under Ground C of the Abortion Act 1967 — that it is better for a woman's mental health to have an abortion than to continue with an unwanted pregnancy. Any challenge to this premise would effectively suggest that most abortions are not justified under the Act.

Reviews of the psychological effects of abortion have arrived at disparate conclusions, which makes the provision of guidance to doctors challenging. Despite some reviews showing that abortion is linked to various adverse mental health outcomes, other reviews say there is no link, failing even to acknowledge controversy in the field, while yet others say social mores are the cause of any mental harm.

One problem with even some of the best known and most widely cited research studies is choosing what groups to compare with women who have an abortion (Women who have had a miscarriage? Given birth? Women who have never been pregnant? With an intended pregnancy or not?) because there is no direct equivalence. Then there is selection bias (many studies have high drop-out rates and low recruitment rates) because those who are least likely to participate will be those most affected by the abortion. And many studies simply fail to follow up women long enough after the initial study (often women cope well initially, but years later reappraise the abortion negatively). (1)

One of the most comprehensive reviews into the mental health outcomes of abortion, carried out in the UK in 2011, found that having an unwanted pregnancy is associated with an increased risk of mental health problems. (2) However, they found that the rates of mental health problems for women with an unwanted pregnancy were the same, whether they had an abortion or gave birth. In other words abortion made no difference to the outcome.

However, the review also found that women who have mental health problems before an abortion are at greater risk of mental health problems afterwards. They also found that several other factors such as stressful life events, pressure from a partner to have an abortion, a negative attitude towards abortions in general and a negative emotional reaction immediately following an abortion, may also have a negative impact on mental health.

The results of this review were re-examined by Prof David Fergusson, who confirmed that although some studies conclude that abortion has neutral effects on mental health, no study has reported that exposure to abortion reduces mental health risks (which should theoretically nullify the use of Ground C for abortions). His own research reports small to moderate increases in risks of some mental health problems post-abortion. (3)

A growing body of evidence suggests that women may be at an increased risk of mental health disorders, notably major depression, substance misuse and suicidality, following abortion, even with no previous history of problems. Researchers not associated with vested interest groups have published this growing scientific evidence. They include Fergusson in New Zealand (4) and Pedersen in Norway. (5)

Researchers who are known to be more 'pro-life' have also published extensively in academic journals on this topic for many years. See for example Sullins, Reardon, Rue and Coleman. (6) Coleman has produced findings suggesting a clear link between abortion and adverse mental health effects. (7) Her findings are striking: nearly 10% of all mental health problems are directly attributable to abortion, and women with an abortion history experience nearly double the risk of mental health problems when compared with women who have not had an abortion. Even compared to women delivering an unintended pregnancy, she found that post-abortion women still have a 55% increased risk of mental health problems.

Coleman's work has strengths and weaknesses. It was published in the British Journal of Psychiatry, passing extensive scrutiny, and is a meta-analysis of 22 published studies, with nearly 900,000 participants. However, it has several methodological weaknesses that have been criticised by researchers who have come to different conclusions. Yet Fergusson, who has described himself as a pro-choice atheist, defends Coleman and concurs with her overall finding: 'There is a clear statistical footprint suggesting elevated risks of mental health problems amongst women having abortions.' (8)

Women have been told that abortion is an emotion-free, quick and safe process requiring a simple operation or a couple of pills. They are entitled to be told that it is more significant than this and that there are associated risks. Many women who present for abortion are ambivalent — a known risk factor for later adverse effects — so it is imperative that health professionals provide all relevant information for their decision-making.

At the very least, they should be told that there is a lack of academic studies showing any benefits from abortion — despite the fact that so many are carried out on the presumption that abortion reduces mental health risks.

Philippa Taylor is CMF Head of Public Policy