Objective: To assess changes in human fertility over time.
Design: Time-trend analyses and age-period-cohort modeling.
Setting: Sweden, 1983-1993.
Patient(s): All primiparous women aged > or =20 years during the study period. There were 401,653 women who were identified through the nationwide Medical Birth Register.
Intervention(s): None.
Main outcome measure(s): Risk of subfertility, defined as > or =1 year of involuntary childlessness.
Result(s): Subfertility problems decreased dramatically over successive maternal birth cohorts. Further, the risk of subfertility increased with age and decreased with increasing formal education.
Conclusion(s): A decrease in male fertility cannot be ruled out on the basis of these results, but if present, it is minor and totally outweighed by other favorable developments. As the main explanation for our findings, we propose a decrease in the prevalence of secondary subfertility as a result of the eradication of gonorrhea.