Figure 1.

From Bonde et al. ⁸ (with permission): 430 couples with no earlier reproductive experience, 20–35 years of age, participated in a study on the association between semen quality and the probability of conception in a single menstrual cycle. The couples discontinued the use of contraception and were followed up for six menstrual cycles or until a pregnancy was verified within this period. Each man was asked to provide a semen sample at enrolment. Women kept a daily record of vaginal bleeding and sexual activity. The association between semen quality and likelihood of pregnancy was assessed by logistic regression adjusted for sexual activity and female factors associated with low fertility. There were 165 (65.0%) among those with a sperm concentration of 40 million per mL and 84 (51.2%) among those with lower sperm concentrations. The probability of conception increased with increase in sperm concentration up to 40 million per mL, but any higher sperm concentration was not associated with the additional likelihood of pregnancy.