Male and female factors in fertility.

Fertility is affected by the age of the female partner, but not that of the male partner, in the age ranges within which most attempts at conception occur. However, the literature on the effect of the smoking status of each partner is inconclusive. As part of a longitudinal study representative of all people born in Britain in 1958, 11,407 people were interviewed in 1991, of whom 3,132 female and 2,576 male cohort members had had or fathered at least one pregnancy. The outcome measure was the time to pregnancy of the first pregnancy (live births only), and the antecedent variables were the cohort member's age at that time and both partner's smoking habits and educational levels. Unadjusted analysis demonstrated that both the time to pregnancy and clinical subfertility were associated with higher maternal but not paternal age and with the smoking habits and educational levels of both parents. Multivariate analysis showed that paternal smoking failed to enter the model if the educational variables were also included. Findings were similar in the two separate analyses on male and female cohort members. This study confirms previous findings on the relative importance of maternal and paternal age in this age range. Maternal smoking affects fertility, but earlier reports of an apparent effect of paternal smoking may be due to confounding with socioeconomic status.