The importance of childbearing for Hodgkin's disease: New evidence from incidence and mortality models

Background. We reported in a recent study that parity was inversely related to the incidence of Hodgkin's disease (HD) in Norwegian women younger than 56. In this study, another data set was used to estimate the parity effects on incidence at higher ages, and two different data sets were used to assess how parity influences prognosis. Methods. Multiplicative hazard models were estimated for incidence. A novel approach, based on mixed additive-multiplicative mortality hazard models, was used to assess differences in prognosis. The analysis was based on register and census data. Results. There was no effect of parity within marriage on HD incidence in women aged 40-80. With respect to prognosis, parity was found to have a beneficial influence in the age group 15-66. Excess mortality among two-child mothers with HD compared to otherwise equal two-child mothers without HD, was significantly lower than the corresponding excess mortality among childless women. However, the same pattern appeared for men. By contrast, there were strong indications of an increase in excess mortality from HD across marital parity for women aged 40-80. Conclusion. The results lend support to the view that childbearing confers no long-term protection, but the evidence is far from clear. The physiological processes triggered by pregnancies do not seem to have a beneficial effect on survival. Childbearing before diagnosis may influence prognosis in men as well as women through social or emotional factors, and may also be related to prognosis because of parity-differentials in the general physical constitution. In addition, there is likely to be a positive selection of individuals who want to and are able to have a child after diagnosis.