Increasing paternal age is associated with delayed conception in a large population of fertile couples: evidence for declining fecundity in older men

The impact of male age on fecundity remains controversial. Here, a large po pulation study was used to investigate the effect of paternal age on time t o conception. All couples in the Avon Health district expecting a baby betw een 1 April 1991 and 31 December 1992 were eligible. Questionnaires complet ed by both the man and the woman at 18 weeks gestation covered specific fer tility factors, e.g. parity, paternity, cohabitation and oral contraception ; and nonspecific factors, e.g. educational achievement, housing, cigarette smoking, alcohol consumption, obesity. Logistic regression was used to ide ntify factors independently related to conception in less than or equal to 6 or less than or equal to 12 months. Of 8515 planned pregnancies, 74% were conceived in less than or equal to 6 months, 14% in the second 6 months an d 12% after more than a year. Nine variables, including the age of the woma n, were independently related to time to conception. After adjustment for t hese, the likelihood of conception within 6 or 12 months was lower in older men. Compared to men <25 years old, the adjusted odds ratios (95% confiden ce interval) for conception in less than or equal to 12 months were 0.62 (0 .40, 0.98), 0.50 (0.31, 0.81) and 0.51 (0.31, 0.86) in men aged 30-34, 35-3 9 and greater than or equal to 40 years respectively.