Evaluation of 304 infertile couples with at least one abnormal semen analysis (sperm density < 20 x 10(6)/ml and/or motility < 50%) and no apparent female factors was performed in a multicentre prospective cohort study. In 73 cases therapeutic donor insemination was performed (TDI group) with a resulting pregnancy rate of 48%. The remaining 231 couples (non-TDI group) had an overall pregnancy rate of 25%. The TDI group had a shorter duration of infertility. The ages of both partners were comparable in TDI and non-TDI groups. In the non-TDI group, univariate analysis resulted in identification of six clinical variables associated with a change in pregnancy rates. The strongest association was noted for length of infertility. There was a weaker association for semen volume, concentration of leukocytes in semen, history of pregnancy in the female partner and laparoscopy. Multiple variable analysis of data from the non-TDI group revealed that independent predictors of pregnancy were 'duration of infertility' and 'history of pregnancy in the female partner'. The multiple variable modelling suggested that (i) an increase in the length of infertility by 1 month prolongs the time to pregnancy by an additional 1.6% (95% confidence interval: 1.5-1.7%); and (ii) a history of past pregnancy in the female partner reduces the time of pregnancy by 51% (95% confidence interval: 47-56%).

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