Does adoption affect subsequent fertility?

A hypothesis derived from the old wives' tale that adoption increases subsequent fertility was tested by analysis of follow-up data obtained from 895 couples who were "at risk" of pregnancy and of adoption after they had registered in the Stanford Infertility Clinic between 1963 and 1977. Of the 767 couples who did not adopt, 329 later conceived; of the 128 who did adopt, 41 later conceived. Simple comparison of the percentages or, indeed, of the life tables suggests reduced fertility after adoption. However, this is probably a spurious effect related to a number of factors which differ between two groups. These differences were controlled in the statistical analysis by methods which take into account the length of time each couple was at risk of either conception or adoption and the presence or absence of explanatory variables. The relative risk of conception estimated by the Cox model was not significantly different from 1 and the Mantel-Haenszel statistic (m = 0.208) indicates no significant difference in subsequent conception rates between adoptive and not-adoptive couples. The same methods were used to control for seven covariates, including age and duration of infertility, which could affect conception rates. In each instance, the estimate of relative risk of conception for adoptive versus not-adoptive couples was not significantly different from 1. Therefore, our data do not support the hypothesis that adoption affects subsequent fertility.