Abortion and Miscarriage Do Not Increase Breast Cancer Risk, Large Study Confirms
A comprehensive Finnish study has found no association between a history of induced abortion or miscarriage and an increased risk of breast cancer, either before or after menopause. The findings, published in Acta Obstetricia et Gynecologica Scandinavica, address a long-standing and often politically charged debate.
Addressing the “Abortion-Breast Cancer Hypothesis”
The research challenges the “abortion–breast cancer hypothesis,” a claim frequently used by abortion opponents suggesting that terminating a pregnancy increases a woman’s risk of developing breast cancer. This hypothesis stems from the observation that breast cancer risk initially increases in the first few years after pregnancy, then decreases with subsequent pregnancies and breastfeeding. The concern was that early pregnancy termination might disrupt this natural process.
Study Methodology and Findings
Researchers led by Oskari Heikinheimo from the University of Helsinki analyzed data from 31,687 women diagnosed with breast cancer between 1972 and 2021, and compared them to 158,433 matched controls. Finland’s legally binding registries for abortions (since 1950) and hospital-treated miscarriages provided robust data. Information on hormone replacement therapy was obtained from a medication prescription register, and socioeconomic status data came from the National Statistics Agency.
The study found that:
- Among premenopausal women, a history of induced abortion showed no increased risk of breast cancer (Odds Ratio [OR] 1.01, 95% Confidence Interval [CI] 0.92-1.10).
- Similarly, miscarriage was not associated with increased risk in premenopausal women (OR 1.02, 95% CI 0.89-1.16).
- Postmenopausal women with a history of induced abortion also showed no increased risk (OR 0.96, 95% CI 0.87-1.07).
- Miscarriage did not influence the risk of breast cancer in postmenopausal women (OR 0.93, 95% CI 0.80-1.09).
- The number of abortions or miscarriages, or the age at the time of first pregnancy loss, did not alter these results.
Confirmation from Previous Research
This study reinforces the findings of a 2024 meta-analysis of 53 studies involving over 83,000 breast cancer patients from 16 countries, published in The Lancet, which also found no link between abortion and increased breast cancer rates. However, the Finnish study’s use of high-quality registry data addresses limitations of previous research that relied on self-reported information and didn’t fully account for factors like hormone replacement therapy.
Finland’s Abortion Laws
Abortion is legal and free of charge upon request in Finland for the first 12 weeks of pregnancy as of September 1, 2023. Prior to this, while widely accessible, the law required women to state their motivations and obtain approval from one or two doctors.
Key Takeaways
- A history of induced abortion or miscarriage does not increase the risk of breast cancer.
- The findings are supported by both a large Finnish registry study and a meta-analysis of global research.
- The “abortion-breast cancer hypothesis” is not supported by scientific evidence.
This research provides further reassurance to women and healthcare providers, debunking a persistent myth and offering evidence-based information regarding breast cancer risk.
Source: Acta Obstetricia et Gynecologica Scandinavica