Background: Studies of body mass index and semen quality have reported mixed results, but almost all were cross-sectional and many were conducted in selected populations. Longitudinal studies in population-based cohorts are necessary to identify how timing and duration of excess adiposity may affect semen quality.
Methods: In 193 members of the Child Health and Development Studies birth cohort, we examined associations of birth weight and adiposity at six time points spanning early childhood and adulthood with sperm concentration, motility, and morphology at mean age 44 years, as well as with corresponding 2010 World Health Organization (WHO) subfertility reference levels.
Results: Birth weight for gestational age percentile was positively associated with square-root sperm concentration (regression coefficient B [95% confidence interval] = 0.02 × 103 sperm/ml [0.004, 0.04]). Overweight/obesity in men's 20s was associated with lower percent progressive motility (B =-5.2 [-9.9, -0.63]), higher odds of low motility (odds ratio (OR) = 2.4 [1.3, 4.4]), and higher odds of poor morphology (OR = 1.9 [0.94, 3.8]). Those who were overweight/obese in their 20s were also more likely to meet two or three WHO subfertility criteria (OR = 3.9 [1.6, 9.4]) compared with normal-weight men. Each additional adult decade in which a participant was overweight/obese was associated with higher odds of low motility (OR = 1.3 [0.96, 1.6]) and higher odds of meeting two or three WHO subfertility criteria (OR = 1.5 [1.0, 2.2]).
Conclusions: In our data, associations among adiposity and sperm concentration, motility, and morphology varied according to timing and duration of exposure, potentially reflecting different biological mechanisms that influence these semen parameters.