Lower total motile count is associated with smaller historic intergenerational family size: a pedigree analysis from the Utah Population Database.

PURPOSE To describe the association between contemporary total motile count (TMC), a measure of male factor infertility, and historic intergenerational family size. METHODS This is a retrospective, population-based, cohort study of men who underwent semen analysis for infertility workup at University of Utah, with at least a single measure of TMC, who were linked to extensive genealogical data. Two thousand one hundred eighty-two pedigree branches of men with a measure of TMC within the UPDB were identified. We identified the average number of generations and offspring within each generation. Conditional logistic regression models were used to assess the association between the risk of having a TMC in the 5th or 25th percentile and intergenerational family size. Generalized estimating equations (GEE) were used to assess the association between interval-level TMC and the number of ancestral offspring. RESULTS We found no association between intergenerational size and TMC within the 5th percentile (TMC < 4 million; RR = 0.97, 95% CI 0.93-1.01) or the 25th percentile (TMC < 62 million; RR = 1.00, 95% CI 0.97-1.03). When TMC was analyzed as a continuous variable, we found that lower TMC is associated with smaller intergenerational family size. For every additional child in their ancestral pedigree, we observed an increase in TMC of 1.88 million (p = 0.03). Men in the top quartile for intergenerational family size had a TMC that was 48 million higher than men in the bottom quartile (p = 0.047). CONCLUSIONS We found an association between TMC and ancestral family size, suggesting that lower TMC is associated with smaller intergenerational family size.