Women’s Health
The association between hypertension during pregnancy and breast cancer later in life varies by complete reproductive history Sage Wyatt* Sage Wyatt Liv Grimstvedt Kvalvik Aditi Singh Rolv Skjaerven Lars Vatten Maria C. Magnus
Background: Previous studies have shown decreased risk of breast cancer later in life after hypertensive disorders of pregnancy (HDP). Most studies analyse HDP as a binary variable, regardless of the number and order of an individual’s pregnancies. This study aims to find the association between breast cancer and complete reproductive history of HDP, considering the context of all pregnancies in an individual’s lifetime.
Methods: We used the Medical Birth Registry of Norway and the Norwegian Cancer Registry. Our exposure included 12 patterns of reproductive history, given HDP in first, second, and later pregnancies. Our outcome was diagnosis of breast cancer after age 45. We used Cox proportional hazard models (aHR) and 95% confidence intervals (CI) with mother’s age as the underlying time variable, adjusted for year of mother’s first birth.
Results: In a cohort of 1,264,571 mothers, 104,737 (8.3%) had HDP at any point in their complete reproductive history. In mothers with 1 birth, we found a protective effect of HDP (HR 0.85, 95%CI 0.78, 0.92). In mothers with 2 births, we found estimates of the association ranged from aHR 0.80 (95%CI 0.70, 0.92) to HR 0.97 (95%CI 0.90, 1.05), with the highest estimate being mothers who had HDP in their first pregnancy and no HDP in their second pregnancy. In mothers with three or more lifetime births, we found estimates of the association ranged from aHR 0.85 (95%CI 0.76, 0.96) to aHR 1.01 (95%CI 0.80, 1.28), with the highest estimate being mothers who had HDP in the first pregnancy, no HDP in the second pregnancy, and HDP in their third or later pregnancy.
Conclusion: We found the strength of the association between HDP and breast cancer depends on a mother’s complete reproductive history. We will continue to investigate these associations, including the role of gestational age at delivery.