ArticlesRelation between semen quality and fertility: a population-based study of 430 first-pregnancy planners
Introduction
Semen analysis has been part of the standard diagnostic routine for infertile couples ever since low sperm count was linked to male infertility. The sperm count remains the standard measure, but there is debate about the importance of sperm concentration in male infertility. In a study of 800 fathers in 1951,1 the lower limit of the normal range of sperm concentration was set at 60×106 spermatozoa per mL seminal fluid. The lower limit has been successively reduced to 20×106/mL,2 which was subsequently adopted by WHO as a guideline to diagnose male infertility.3 Routine semen analysis also includes measures of sperm morphology and motility, which may have significant effects on male fertility.4
Previous studies of semen characteristics and male infertility were limited because they included only infertile couples or only men who had fathered a child.1, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 Some of these studies did not take account of time gaps between semen analysis and fertility assessment, or lacked information on female infertility and sexual activity. To address these issues, we studied the relation between semen characteristics and the probability of pregnancy for couples who had no previous reproductive experience.
Section snippets
Participants
In 1992–94 we wrote to 52 255 Danish trades-union members (metalworkers, office workers, nurses, day-care workers) aged 20–35 years, who lived with a partner and had no children. Couples were eligible for the study if they had no previous reproductive experience, and now intended to stop contraception and have children. Couples were ineligible if they had ever deliberately tried to have a child, whether successfully or not, if the woman had ever miscarried, had an induced abortion, or given
Participants' and semen characteristics
35 couples of the 430 withdrew from the study before the woman became pregnant (table 1); 20 because of changes to family plans, and 15 because of azoospermia, amenorrhoea, or anovulation. 12 men did not provide a semen sample at enrolment.
Characteristics of semen samples are given in table 2. Paired analysis showed that the mean sperm concentration of frozen follow-up samples was 7·6% lower than that of unfrozen enrolment samples (p=0·17), the mean volume was 14·2% larger (p=0·0001), and the
Discussion
This study has linked semen quality with the probability of conception among first-pregnancy planners. Low sperm concentrations were strongly associated with low likelihood of pregnancy. We set a sperm concentration of 40×106/mL as a reasonable threshold between subfertile and fertile men, since any higher sperm concentration was not associated with increased likelihood of pregnancy. However, the 95% CI around this threshold was broad and included a concentration of 20×106/mL—the upper limit of
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