Finnish Registry Study Finds No Link Between Abortion, Miscarriage, and Breast Cancer Risk

A large nationwide study from Finland adds robust evidence to a longstanding and often politicized debate: neither induced abortion nor miscarriage appears to increase a woman’s subsequent risk of breast cancer.

In research published in Acta Obstetricia et Gynecologica Scandinavica, investigators analyzed data from 31,687 women diagnosed with breast cancer between 1972 and 2021 and 158,433 matched controls drawn from national population registries . Using high-quality, mandatory reporting systems, the team examined whether a history of induced abortion or miscarriage was associated with the risk of premenopausal (younger than 50 years) or postmenopausal (50 years or older) breast cancer.

After adjusting for established risk factors—including age at first birth, socioeconomic status, occupational physical activity, and, in postmenopausal women, hormone therapy use—the findings were consistent and largely null.

Among premenopausal women, a history of induced abortion was not associated with increased breast cancer risk (odds ratio [OR] 1.00; 95% confidence interval [CI] 0.92–1.09). Similarly, no increased risk was observed in postmenopausal women (OR 0.95; 95% CI 0.86–1.06) . The pattern was the same for miscarriage: OR 1.02 (95% CI 0.89–1.16) in premenopausal women and 0.92 (95% CI 0.79–1.08) in postmenopausal women .

Importantly, risk did not vary significantly by the number of abortions or miscarriages, nor by age at the time of first pregnancy loss. One exception—a modestly elevated risk of postmenopausal breast cancer among women whose first induced abortion occurred before age 20 (OR 1.21; 95% CI 1.01–1.46)—was interpreted cautiously by the authors, who noted the long interval between exposure and diagnosis and the possibility of a chance finding .

The study’s scale and methodological rigor distinguish it from much of the earlier literature. Many previous investigations relied on self-reported reproductive histories and were vulnerable to recall bias. In contrast, Finland’s national registries mandate reporting of induced abortions since 1950 and systematically capture miscarriage diagnoses treated in public healthcare settings. Controls were matched by birth year and parity, and analyses accounted for key confounders known to influence breast cancer risk .

The validity of the dataset was reinforced by expected associations observed in the study. Early age at first birth was protective, particularly for premenopausal breast cancer, and longer duration of postmenopausal hormone therapy—especially regimens including continuous progestin—was associated with increased risk . These patterns are consistent with established epidemiologic evidence.

While the investigators lacked data on certain variables, such as age at menarche, alcohol use, and body mass index, the comprehensive adjustment for major reproductive and hormonal factors strengthens confidence in the findings.

Globally, induced abortion and miscarriage are common experiences. The authors conclude that concerns about increased breast cancer risk should not influence counseling or clinical care for early pregnancy termination or loss . For clinicians and patients alike, the message from this large registry-based analysis is clear: early pregnancy loss, whether induced or spontaneous, does not confer an elevated risk of subsequent breast cancer.