Do parental factors affect male and female fertility?

There is little published evidence on parental characteristics and the fertility of their offspring of either sex. Maternal smoking has been reported to reduce fertility in both sexes and was also suggested to be relevant to the health of the male reproductive system on the basis of descriptive epidemiology. We undertook a cohort study based on a sample representative of the British population born in 1958 who have been followed up since birth. The outcome variable was time to pregnancy measured in months, up to age 33 years. Antecedent variables were the age of both parents; maternal smoking, height, prepregnancy body mass index, and parity; and paternal social class (manual/nonmanual labor). First births to cohort members were analyzed using a Cox logistic model for discrete survival times. A total of 1,714 and 2,587 values of time to pregnancy were available, respectively, for male and female cohort members. In the unadjusted analyses, all odds ratios were in the range 0.9-1.1, apart from the father's social class. In the adjusted analyses, this effect also disappeared. We conclude that the observed heterogeneity in biological fertility is unrelated to those characteristics of parents that we were able to analyze.