Objective: A population-based matched survival study was conducted to assess the risk of death for breast cancer patients in relation to whether they were delivered of a live born child subsequent to the cancer diagnosis.
Study design: Among the 2548 women < 40 years old diagnosed with carcinoma of the breast in 1967 to 1989 in Finland there were 91 eligible patients with subsequent deliveries (> or = 10 months after the diagnosis) for whom 471 controls were matched for stage, age, and year of breast cancer diagnosis. The controls had to have survived at least the interval between the diagnosis and the delivery of their matched counterparts. The follow-up started from the date of the first delivery after the diagnosis or after the corresponding interval for the matched controls. A stratified Cox proportional hazards survival analysis was performed.
Results: The controls had a 4.8-fold (95% confidence interval 2.2 to 10.3) risk of death compared with those who were delivered after the diagnosis of breast cancer.
Conclusion: Our interpretation of this result is a "healthy mother effect" (i.e., that only women who feel healthy give birth and those who are affected by the disease do not). Nevertheless, six of eight deaths among the 91 patients who did give birth were related to breast cancer.