(959) The Protective Power of Parity: Long-Term Risk Reduction in Gynecologic Malignancies

Parity has long been recognized as a key factor influencing gynecologic malignancy risk, likely due to hormonal exposures and tissue remodeling due to pregnancy. While prior studies suggest higher parity may be protective, findings vary. We aimed to assess the relationship between maternal parity and the long-term risk of breast, uterine, and ovarian cancers.

Study Design:
A retrospective cohort study of women who delivered in a tertiary center between 1991–2021 was conducted. Women were stratified by parity at final pregnancy (from primiparous to parity≥6), and gynecologic cancer diagnoses were assessed using ambulatory and hospitalization records. Kaplan-Meier survival curves were used to compare cumulative gynecologic malignancy incidence, and Cox regression models were performed to adjust for confounders. 

Results:

Among 28,642 women included, 810 (2.8%) women subsequently developed a gynecologic malignancy. Among all women in the cohort, multiparous women (≥6 births) had the lowest rates of gynecological cancers (Table). Similarly, women with parity ≥6 presented with the lowest cumulative incidence of gynecological malignancies (Figure). This association remained significant in a Cox proportional hazards model which adjusted for ethnicity and the use of fertility treatments, with parity ≥6 demonstrating a protective effect with significantly lower risk of gynecologic malignancy as compared to primiparous women (Table).

Conclusion:
Among all the women included in this study, only those with more than 5 deliveries benefited from the protective effect of parity against the development of gynecological malignancy. However, a non-significant reduction of malignancy risk was also noted for women with more than 3 deliveries, supporting the protective role of recurrent deliveries.