Fertility and offspring sex ratio of men who develop testicular cancer: a record linkage study

Analysis of associations between testicular cancer, subfertility and offspring sex ratio (proportion of males born among newborns) was performed on 3530 Danish men, born 1945-1980, who developed testicular cancer in the period 1960-1993, As the basis of comparison we used the total population of Danish men born in the period 1945-1980 (n = 1 488 957) and their biological children (n = 1 250 989), Men who developed testicular cancer had, prior to the cancer diagnosis, a reduced fertility (standardized fertility rate ratio: 0.93, 95% confidence interval: 0.89-0.97) and a significantly lower proportion of boys (48.9%, P = 0.02) compared with the general population (51.3%). The reduction in fertility was more pronounced in men with non-seminoma but the reduction in offspring sex ratio was independent of histological type. This confirms earlier results from less conclusive studies and indicates that testicular cancer, male subfertility and a female-biased sex ratio among new-born infants are characteristics of male reproduction that are linked by biological mechanisms.