Time to pregnancy and occupational lead exposure

Background: Lead exposure is known to be harmful to the male reproductive system, including impairment of fertility. However, it is unclear whether currently existing low levels of exposure have this effect. Aims: To study retrospectively current workers in lead using industries (battery manufacture, smelting, etc), and in non-lead using control industries, in four European countries, with Time To Pregnancy as the outcome variable, as part of the EU funded Asclepios Project. Methods: Exposure assessment was mainly by blood lead values, which were available from the late 1970s, supplemented by imputed values where necessary. Three exposure models were studied: (1) short term (recent) exposure; (2) total duration of work in a lead using industry; and (3) cumulative exposure. A Cox proportional hazards model with discrete ties was used for the statistical analysis, with covariates for both partners. Results: A total of 1104 subjects took part, of whom 638 were occupationally exposed to lead at the relevant time. Blood lead levels were mainly less than 50 mug/dl. No consistent association of Time To Pregnancy with lead exposure was found in any of the exposure models, although reduced fertility was observed in one category each in models (2) and (3). Conclusions: This basically negative result is unlikely to be due to the misclassification of key variables, to insufficient statistical power, or to bias, for example, response bias. If any impairment of male reproductive function exists at the levels of occupational lead exposure now current, it does not appear to reduce biological fertility.