Birth by caesarean section and semen quality in adulthood: a Danish population-based cohort study

BackgroundThe caesarean section (CS) rate has increased worldwide and there is an increasing public and scientific interest in the potential long-term health consequences for the offspring. CS is related to persistent aberrant microbiota colonization in the offspring, which may negatively interfere with sex hormone homeostasis and thus potentially affect the reproductive health. It remains unknown whether adult sons' semen quality is affected by CS. We hypothesize that CS is associated with lower semen quality.MethodsThis study was based on the Fetal Programming of Semen Quality cohort (FEPOS, enrolled from 2017 to 2019) nested within the Danish National Birth Cohort (DNBC, enrolled from 1996 to 2002). A total of 5697 adult sons of mothers from the DNBC were invited to the FEPOS cohort, and 1044 young men participated in this study. Information on mode of delivery was extracted from the Danish Medical Birth Registry, and included vaginal delivery, elective CS before labor, emergency CS during labor and unspecified CS. The young men provided a semen sample for analysis of semen volume, sperm concentration, motility and morphology. Negative binomial regression models were applied to examine the association between CS and semen characteristics with estimation of relative differences in percentages with 95% confidence intervals (CIs).ResultsAmong included sons, 132 (13%) were born by CS. We found a slightly lower non-progressive sperm motility (reflecting higher progressive sperm motility) among sons born by CS compared to sons born by vaginal delivery [relative difference (95% CI): - 7.5% (- 14.1% to - 0.4%)]. No differences were observed for other sperm characteristics. When CS was further classified into elective CS, emergency CS and unspecified CS in a sensitivity analysis, no significant differences in non-progressive motility were observed among sons born by any of the three types of CS compared to sons born vaginally.ConclusionsThis large population-based cohort study found no significant evidence for an adverse effect on semen quality in adult sons born by CS. Caesarean section is one of the most frequently used interventions during childbirth and global cesarean delivery rates continue to increase. The rising cesarean delivery rate has been reported to be related with series of adverse health outcomes in children, such as asthma, allergies, obesity, diabetes and even poor emotional, behavioral and educational outcomes. Still, it remains unknown whether children's reproductive health is affected by this delivery mode.Based on data from the Fetal Programming of Semen Quality cohort (FEPOS,) nested within the Danish National Birth Cohort, we have therefore analyzed the potential effect of caesarean section on son's semen quality in 1044 young men. We found a slightly higher progressive sperm motility among sons born by caesarean section compared to sons born by vaginal delivery. No differences, however, were observed for semen volume, sperm concentration and morphology between the two delivery modes.The FEPOS cohort is the largest population-based male offspring cohort worldwide. This is the first study aiming to examine the association between caesarean section and semen quality in adulthood. Although the findings need to be confirmed in other studies, it is reassuring that this large population-based cohort study finds no significant evidence for an adverse effect on semen quality in adult sons born by caesarean section.