Scientific evidence doesn’t support the claim that induced abortion increases the risk of breast cancer and mental illness

On 18 May 2022, Newsmax posted to its Facebook page an excerpt of an interview with two physicians, Christina Francis, the chair of the American Association of Pro-Life Obstetricians and Gynecologists (AAPLOG), and George Delgado, who also sits on the board of directors at AAPLOG. Delgado has promoted scientifically unsubstantiated claims that medical abortion can be reversed (abortion reversal).

During the interview, Francis and Delgado made several allegations regarding the harms of abortion, specifically that abortion increases a woman’s risk of breast cancer, mental illness, and preterm labor.

Health Feedback reached out to the American College of Obstetricians and Gynecologists (ACOG), a professional association of physicians specializing in obstetrics and gynecology in the U.S., for comment regarding the scientific accuracy of these claims. In an email, a spokesperson for ACOG stated that “Abortion does not increase the risk of breast cancer, depression, or infertility” and that “ACOG affirms that these are lies and are proven to be untrue.”

The aim of this review is to examine the scientific evidence for the claims made by Francis and Delgado. As part of our assessment of the credibility of these claims, our review will also include relevant clinical guidance and position statements by trusted medical and scientific authorities, such as ACOG, the U.S. National Cancer Institute, and the American Psychological Association.

Scientific studies haven’t detected an increased risk of breast cancer following induced abortion

The beginnings of the claim that having an abortion increases the risk of breast cancer can be traced back to a study in rats published in 1980. Researchers induced breast cancer in rats by aborting their pregnancies and then exposing them to a chemical 7,12-dimethylbenz(a)anthracene (DMBA), a powerful carcinogen that can induce breast cancer in rats. They reported that rats which remained pregnant didn’t develop breast cancer, while 77% of rats that had their pregnancy aborted developed breast cancer^[1].

Some case-control studies, which reported that women who had an abortion were at an increased risk of developing breast cancer, appeared to corroborate the rat studies. In such studies, researchers ask healthy women and women with breast cancer whether they had an induced abortion, then compare the incidence of breast cancer in the two groups.

However, case-control studies are poorly adapted for such studies, because of their retrospective quality and the sensitive nature of abortion. The stigma associated with induced abortion means that women may not admit to having one, particularly healthy women.

This means that the number of induced abortions recorded among healthy women is likely to be underestimated. This would make it seem as if more women with breast cancer had induced abortions, creating the appearance of an association where there is none.

This is also known as response bias, as illustrated in an article in Discover Magazine:

“[P]atients are always looking for clues to their illnesses, and so ‘women who have breast cancer will search their souls, and be very likely to search deeply in their memories, and disclose things that might be embarrassing,’ says David Grimes, clinical professor of obstetrics, gynecology, and epidemiology at the University of North Carolina School of Medicine in Chapel Hill. ‘But a woman who does not have the disease and is picked at random from the community is very unlikely to disclose to an anonymous researcher knocking on the door that she had an abortion in 1992.’”

ACOG also cautioned people about the same bias:

“A key methodological consideration in interpreting the evidence for any relationship between abortion and breast cancer risk is the sensitive nature of abortion, which could affect the accuracy in retrospective studies that rely on participant reports of having had an abortion.”

The U.S. National Cancer Institute remarked on the state of research that appeared to show an association between breast cancer and abortion:

“Most of these studies, however, were flawed in a number of ways that can lead to unreliable results. Only a small number of women were included in many of these studies, and for most, the data were collected only after breast cancer had been diagnosed, and women’s histories of miscarriage and abortion were based on their ‘self-report’ rather than on their medical records.”

At this point, readers may raise the question of how large of a problem response bias can be. There have been some studies addressing this issue. Two researchers in the Netherlands analyzed data from more than 900 women residing in one of two regions that differ from each other in prevalence and attitude to abortion^[2]. They reported a much higher risk of breast cancer in women who’d had an induced abortion in the southeastern region, which was predominantly Roman Catholic, compared to the western region, suggesting response bias. This was corroborated by the reporting rates of oral contraceptive use, with women in the southeastern regions underreporting the duration of their oral contraceptive use by 6.3 months longer than women living in the western region, indicating response bias.

These results are corroborated by a study in Sweden^[3]. This study was also retrospective—like the above studies, researchers surveyed healthy women and women with breast cancer to determine if they had an abortion—but in this case, researchers checked the national registry of legal abortions and compared women’s responses to registry records to determine if the women had been truthful. The researchers found that:

“There were 26 cancer cases and 44 controls reporting abortions, but 24 cases and 59 controls with abortions in the registry. The ratio Q between these odds ratios was 1.5, indicating bias. There was no evidence of selective forgetfulness by cases. Probably because of the sensitive nature of abortion, and the seriousness of malignant disease, reporting of abortion was more accurate among breast cancer cases, suggesting underreporting by healthy controls.”

Since then, researchers have turned to prospective studies, which monitor people before they’ve developed the disease. This design ensures that the study isn’t affected by the kind of response bias illustrated above. More importantly, such studies haven’t found any association between breast cancer and induced abortion.

One notable example of such a prospective study was conducted in Denmark, which included 1.5 million women^[4]. The study, which was published in the New England Journal of Medicine, reported no overall effect on the risk of breast cancer.

The Collaborative Group on Hormonal Factors in Breast Cancer, chiefly formed by scientists at Oxford University, reviewed 53 studies that included more than 80,000 women. It also reported that pregnancies that ended in an induced abortion don’t increase a woman’s risk of breast cancer^[5].

Overall, the studies that suggest that induced abortion increases the risk of breast cancer are affected by problems like response bias that call the validity of their conclusions into question. By contrast, studies that mitigate such bias find no association between induced abortion and breast cancer.

Scientific evidence demonstrates that there is no increase in risk of mental health problems following induced abortion

In particular, Coleman published a review in the British Journal of Psychology, in which she analyzed 22 studies, including more than 870,000 women, of whom more than 163,000 had an abortion^[6]. Based on her analysis, Coleman concluded that “Women who had undergone an abortion experienced an 81% increased risk of mental health problems, and nearly 10% of the incidence of mental health problems was shown to be attributable to abortion”.

Coleman’s review was criticized in no fewer than seven letters to the journal, in which multiple groups of researchers pointed out serious methodological flaws (letters 1, 2, 3, 4, 5, 6, 7). Among some of the problems with the review was the fact that it didn’t provide the search strategy used to identify relevant literature; it didn’t tell readers what the inclusion criteria for studies were; it didn’t evaluate the quality of the studies; more importantly, it came to conclusions that weren’t substantiated by its own data.

In their letter^[7], Littell and Coyne pointed out the problem of high heterogeneity in the review that Coleman ignored:

“Coleman’s conclusion that the results of the studies in her review are ‘quite consistent’ (p. 183) is belied by visual inspection of the Forest plots, which include non-overlapping confidence intervals. Coleman should have reported results of heterogeneity tests (chi-squared and I2), which probably would have shown significant heterogeneity in results across studies.”

Heterogeneity is a measure that tells us whether the results of the studies in a meta-analysis are consistent with each other. In an article for the BMJ, Higgins et al. explain that “Assessment of the consistency of effects across studies is an essential part of meta-analysis^[8]. Unless we know how consistent the results of studies are, we cannot determine the generalisability of the findings of the meta-analysis”. Low heterogeneity indicates that the results are more consistent with each other and that researchers can have confidence in the results; high heterogeneity indicates the opposite.

In addition, of the 22 studies included in the review, 11 were authored or co-authored by Coleman herself, which raises the question of bias in her interpretation of the results. Compounding the problem of bias is the fact that Coleman didn’t disclose her conflicts of interest. Littell and Coyne:

“Coleman has at least two types of conflict of interest here. Among the most important of such conflicts is an agenda-driven bias, by which authors seek to influence legislation and social policy. David Reardon is a co-author with Coleman on seven articles included in the review and an author on an additional study in the review that does not involve Coleman as a co-author. Reardon is quite explicit about his agenda to instil fear of abortion as a way of facilitating passage of anti-abortion legislation.”

Goldacre and Lee^[9] likewise noted the same failure to disclose conflict of interest, citing a presentation Coleman gave with AAPLOG (the same organization to which Francis and Delgado belong):

“It seems that Professor Coleman is an anti-abortion campaigner, who has previously expressed the view that campaigning should include work in academic journals.”

Coleman’s attempt to establish a causal link between induced abortion and mental health issues is misleading, given that she didn’t account for confounding factors. One significant consideration is that women who seek an induced abortion are more likely to carry unintended pregnancies, while women who go on to deliver are more likely to have intended pregnancies. The circumstances surrounding unintended pregnancies themselves are potentially linked to mental health outcomes. As Polis et al. pointed out, the “effects of unintended pregnancy are difficult to disentangle from effects of abortion”^[10].

Howard et al. also pointed out that the studies included by Coleman in the review generally neglected to account for pre-existing mental illness and other key confounders like social deprivation, whereas studies that do account for such risk factors have “found no significant links between abortion and subsequent poor mental health”^[11].

One notable example is a study by Munk-Olsen et al., published in the New England Journal of Medicine, which examined information in Danish national databases for more than 950,000 girls and women with no record of mental disorders between 1995 and 2007 and who had a first-trimester induced abortion or a first childbirth during that period^[12]. The researchers then estimated the rate of mental illness in the 9 months preceding abortion or birth and the 12 months following abortion or birth. Note that, unlike many of the studies included in Coleman’s review, this method accounts for individuals’ risk factors for psychiatric problems, such as genetic predisposition to such problems, rape history, and social deprivation.

Munk-Olsen et al. found that the incidence of psychiatric problems was similar before and after abortion, meaning that induced abortion isn’t causally associated with mental health problems.

A review of the scientific literature on the subject from 1989 to 2008, led by Major et al., also reported that “the relative risk of mental health problems among adult women who have a single, legal, first-trimester abortion of an unwanted pregnancy is no greater than the risk among women who deliver an unwanted pregnancy”^[13]. It also noted that:

“A history of mental health problems prior to pregnancy emerged as the strongest predictor of postabortion mental health. It is important to note that many of these same factors also are predictive of negative psychological reactions to other types of stressful life events, including childbirth, and hence are not uniquely predictive of psychological responses following abortion.” [emphasis added]

In the American Psychological Association’s position statement on abortion:

“Currently, available evidence does not support that having an abortion is associated with an increase in depressive, anxiety, or post-traumatic stress symptoms”.

ACOG states:

“Lack of abortion access has a significant impact on mental health. Evidence suggests that people are more likely to experience psychological issues, including depression and anxiety, when denied an abortion. One recent study also shows that nearly all people who have an abortion report that it was the right decision for them five years later.”

Induced abortion has been associated with an increased risk of preterm labor, but may be mainly associated with surgical abortion

ACOG defines preterm labor as “labor that starts before 37 weeks of pregnancy”, although preterm labor doesn’t necessarily lead to preterm birth. Among some of the risk factors for preterm labor are past gynecologic conditions or surgeries and a risk factor for preterm birth is past procedures on the cervix. Certain procedures conducted during an abortion, such as dilation and curettage (D&C), do fall within such categories. As such, it is possible for an induced abortion to contribute to the risk of preterm labor and preterm birth.

The question of whether induced abortion is associated with an increased risk of preterm labor is another contentious one. Some studies reported no association between the two^[14,15], while other studies reported a higher risk of preterm birth if a woman had an induced abortion. For example, a case-control study in Europe examined 60 maternity units from ten European countries (total of 2,938 cases of preterm birth and 4,781 babies at term)^[16]. It reported that “Previous induced abortions were significantly associated with preterm delivery and the risk of preterm birth increased with the number of abortions”.

However, the study also noted that procedures used to perform abortions have changed over time, with surgical techniques being predominant during the study period. But given the advent of drug-based abortion methods, the association between induced abortion and preterm labor may change.

A review and meta-analysis by Saccone et al., analyzing 36 studies that include more than one million women, may corroborate the suggestion that the risk mainly comes from gynecological surgery in general, and not elective termination of pregnancy specifically. Notably, the review by Saccone et al. didn’t only include induced abortions, but also miscarriages for which surgery was necessary^[17]. Such a procedure can become necessary to prevent infection and potential blood clotting disorders, which can be fatal^[18].

The review concluded that “Prior surgical uterine evacuation” is an independent risk factor for preterm birth. The authors concluded that their findings “warrant caution in the use of surgical uterine evacuation” and “encourage safer surgical techniques as well as medical methods”. Whether drug-based methods of abortion would carry the same risks as surgical methods is unclear.

Conclusion

Reliable scientific studies so far haven’t found that induced abortion is associated with an increased risk of breast cancer and mental illness. Scientists have found that studies which do suggest an association tend to be affected by methodological problems and bias. These problems call the validity of these studies into question. Some studies detected an association between induced abortions and a higher risk of preterm labor, while others haven’t. However, the increased risk may potentially be linked to certain surgical procedures used in induced abortion, as past gynecological surgery in general is a risk factor for preterm labor. Studies are needed to determine if medical methods of abortion would present a different risk profile.

UPDATE (24 May 2022):

After our review was published, Newsmax corrected its Facebook post that contained these inaccurate claims (see archive of Facebook post containing correction here).

REFERENCES

• 1 – Russo and Russo. (1980) Susceptibility of the mammary gland to carcinogenesis. II. Pregnancy interruption as a risk factor in tumor incidence. American Journal of Pathology.
• 2 – Rookus and Van Leeuwen. (1996) Induced Abortion and Risk for Breast Cancer: Reporting (Recall) Bias in a Dutch Case-Control Study. Journal of the National Cancer Institute.
• 3 – Lindefors-Harris et al. (1991) Response Bias in a Case-Control Study: Analysis Utilizing Comparative Data Concerning Legal Abortions from Two Independent Swedish Studies. American Journal of Epidemiology.
• 4 – Melbye et al. (1997) Induced Abortion and the Risk of Breast Cancer. New England Journal of Medicine.
• 5 – Collaborative Group on Hormonal Factors in Breast Cancer. (2004) Breast cancer and abortion: collaborative reanalysis of data from 53 epidemiological studies, including 83 000 women with breast cancer from 16 countries. The Lancet.
• 6 – Coleman (2018) Abortion and mental health: quantitative synthesis and analysis of research published 1995–2009. British Journal of Psychiatry.
• 7 – Littell and Coyne. (2018) Abortion and mental health: guidelines for proper scientific conduct ignored. British Journal of Psychiatry.
• 8 – Higgins et al. (2003) Measuring inconsistency in meta-analyses. BMJ.
• 9 – Goldacre and Lee. (2018) Abortion and mental health: guidelines for proper scientific conduct ignored. British Journal of Psychiatry.
• 10 – Polis et al. (2018) Abortion and mental health: guidelines for proper scientific conduct ignored. British Journal of Psychiatry.
• 11 – Howard et al. (2018) Abortion and mental health: guidelines for proper scientific conduct ignored.  British Journal of Psychiatry.
• 12 – Munk-Olsen et al. (2011) Induced First-Trimester Abortion and Risk of Mental Disorder. New England Journal of Medicine.
• 13 – Major et al. (2009) Abortion and Mental Health: Evaluating the Evidence. American Psychologist.
• 14 – Frank et al. (1991) The effect of induced abortion on subsequent pregnancy outcome. British Journal of Gynecology.
• 15 – Raatikainen et al. (2006) Induced Abortion: Not an Independent Risk Factor for Pregnancy Outcome, But a Challenge for Health Counseling. Annals of Epidemiology.
• 16 – Ancel et al. (2004) History of induced abortion as a risk factor for preterm birth in European countries: results of the EUROPOP survey. Human Reproduction.
• 17 – Saccone et al. (2015) Prior uterine evacuation of pregnancy as independent risk factor for preterm birth: a systematic review and metaanalysis. American Journal of Obstetrics and Gynecology.
• 18 – Griebel et al. (2005) Management of Spontaneous Abortion. American Family Physician.