Long-term mortality and incidence of cancer after pregnancy-related venous thrombosis: Results of a population-based cohort study

The long-term mortality and incidence of cancer after pregnancy-related venous thrombosis (VT) is not known. In this population-based cohort study we identified women with a first-ever pregnancy-related VT (cases, n = 557)) from 18 Norwegian hospitals during 1990-2003. Hospital controls (n = 1214) were selected among women who gave birth at the same time as a case. All participants were linked to the Norwegian Cause of Death Registry and to the Cancer Registry of Norway in 2012. The general age-adjusted Norwegian female population was used as a second control group to calculate the standardized mortality ratio (SMR) and the standardized incidence ratio (SIR) for cancer. Ten cases (1.8%) and seven hospital controls (0.6%) died during follow-up. Mortality was 3.2 times higher among cases as compared with hospital controls when adjusted for age (HR 3.2, 95% confidence interval 1.2-8.5, p = 0.018). The SMR for the first year of follow-up was 18.8 (7.8-45.3) and for the rest of the study period 0.9 (0.4-2.0). Fifteen cases (2.7%) and 13 hospital controls (1.1%) were diagnosed with cancer after index pregnancy. The incidence of cancer was 2.6 times higher among cases compared with hospital controls when adjusted for age (HR 2.6, 1.3-5.6, p = 0.011), but compared with the age-adjusted female population in Norway there was no excess risk of cancer (SIR 1.0, 95% CI 0.6-1.7). Mortality and incidence of cancer after pregnancy-related VT was low. Both were increased among cases compared with hospital controls, but not when compared with the general population, except for mortality during the first year after VT.