Male factor infertility and risk of death: a nationwide record-linkage study.

STUDY QUESTION: What is the risk of death among men with oligospermia, unspecified male factor and azoospermia in the years following fertility treatment? SUMMARY ANSWER: No significantly elevated risk was observed among men with oligospermia and unspecified male factor, while an increased risk was found among men with azoospermia. WHAT IS KNOWN ALREADY: Previous studies have shown associations between male factor infertility and risk of death, but these studies have relied on internal reference groups and the risk of death according to type of male infertility is not well characterized. STUDY DESIGN, SIZE, DURATION: In this prospective record-linkage cohort study, we identified men who had undergone medically assisted reproduction (MAR) between 1994 and 2015. Data was linked to the Danish causes of death register and sociodemographic registers through personal identification numbers assigned to all Danish citizens at birth. PARTICIPANTS/MATERIALS, SETTING,
METHODS: Men that had undergone MAR in Denmark (MAR Cohort; n = 64 563) were identified from the Danish IVF register, which includes data on whether infertility was due to male factor. For each man in the MAR cohort, five age-matched men who became fathers without fertility treatment were selected from the general population (non-MAR fathers; n = 322 108). Men that could not adequately be tracked in the Danish CPR register (n = 1259) and those that were censored prior to study entry (n = 993) were excluded, leaving a final population of 384 419 men. Risk of death was calculated by Cox regression analysis with age as an underlying timeline and adjustments for educational attainment, civil status and year of study entry. The risk of death was compared among men with and without male factor infertility identified from the IVF register (internal comparisons) as well as to the non-MAR fathers (external comparison). MAIN RESULTS AND THE ROLE OF CHANCE: The risk of death between the MAR cohort (all men, regardless of infertility) and the non-MAR fathers was comparable [hazard ratio (HR), 1.07; 95% CI, 0.98-1.15]. When the MAR cohort was limited to infertile men, these men were at increased risk of death [HR, 1.27; 95% CI, 1.12-1.44]. However, when stratified by type of male factor infertility, men with azoospermia had the highest risk of death, which persisted when in both the internal [HR, 2.30; 95% CI, 1.54-3.41] and external comparison [HR, 3.32; 95% CI, 2.02-5.40]. No significantly elevated risk of death was observed among men with oligospermia [HR, 1.14; 95% CI, 0.87-1.50] and unspecified male factor [HR, 1.10; 95% CI, 0.75-1.61] compared with the non-MAR fathers. The same trends were observed for the internal comparison. LIMITATIONS, REASONS FOR CAUTION: Duration of the follow-up was limited and there is limited generalizability to infertile men who do not seek fertility treatment. WIDER IMPLICATIONS OF THE
FINDINGS: Using national health registers, we found an increased risk of death among azoospermic men while no increased risk was found among men with other types of infertility. For the azoospermic men, further insight into causal pathways is needed to identify options for monitoring and prevention. STUDY FUNDING/COMPETING INTEREST(S): This study is part of the ReproUnion collaborative study, co-financed by the European Union, Interreg V ÖKS. C.G.'s research stay at Stanford was funded by grants from the University of Copenhagen, Kong Christian den Tiendes Fond, Torben og Alice Frimodt Fond and Julie Von Müllen Fond. M.E. is an advisor for Sandstone and Dadi. All other authors declare no conflict of interests. TRIAL REGISTRATION NUMBER: Not relevant.