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Many reproductive failures tend to repeat themselves within the same couple. Whether fecundability (the probability of conceiving in a given number of menstrual cycles) follows the same pattern is studied using data from the European Studies on Infertility and Subfecundity (ESIS): 6630 women were interviewed on 'time to pregnancy' (TTP) and other aspects of their pregnancy history. Surveys were conducted between 1991 and 1994 in seven regions from five European countries. Furthermore, the pattern of fecundability in this population was compared with results from computer simulations based upon a population with fixed fecundability parameters. Results from ESIS speak in favour of the stability of fecundability in the relatively short reproductive life of a couple. However, a substantial proportion of couples with up to two events of subfecundability (TTP >9.5 months) became pregnant shortly after trying again. This finding calls for reservation in starting expensive and/ or unpleasant diagnostic procedures at an early stage when a couple tries to become pregnant again. [ABSTRACT FROM AUTHOR]

Shift work has been associated with various unfavorable pregnancy outcomes (ie, pregnancy loss, spontaneous abortion, low birth weight, etc). The suggested underlying mechanism is the interference of shift work with the circadian regulation of human metabolism and, in particular, with the temporal pattern of endocrine function. To analyze the effect of shift work on fecundity, the Time of Unprotected Intercourses (TUI) has been measured in couples recruited in the European Studies on Infertility and Subfecundity, which were undertaken in seven European countries. A low (odds ratio < 2.0) but consistent excess risk of subfecundity (TUI > or = 9.4 months) has been observed both in a representative sample of the general population of women in reproductive age and in a sample of pregnant women or women who had just given birth. The excess risk was also consistently evident both in the subsample of the first pregnancies and in the subsample of the most recent pregnancies. Only the exposure of women to shift work seemed to affect a couple's fecundity; men working shift work did not modify the fecundity pattern of their own couples. No specific job title among shift workers concentrated the risk of subfecundity. No association of menstrual disorders with shift work was identified. Even though residual confounding could partly account for the results and the fact that a plausible biological explanation of the claimed effect is still lacking, data from this study are in favor of an association between shift work and prolonged waiting time to pregnancy.