Exposure to prenatal paternal smoking tied to lower sperm count in male offspring
In addition to the known evils of maternal smoking during pregnancy on the sons' semen quality, prenatal exposure to paternal smoking can also be harmful, according to data from the large Danish National Birth Cohort (DNBC) presented at the ESHRE 2019 Meeting.
Prenatal exposure to paternal smoking was associated with reductions in total sperm count and concentration in the sons, and this was independent of maternal smoking and after adjusting for potential prenatal confounding factors, reported lead investigator Dr Sandra Søgaard Tøttenborg from Bispebjerg Frederiksberg Hospital in Copenhagen, Denmark.
The population-based follow-up analysis involved 536 19-year-old young men whose mothers were enrolled in the DNBC between 1996 and 2002. Smoking status of both the father and mother were maternal-reported during week 16 of gestation. Semen quality sampled from the young men was characterized based on WHO criteria. [ESHRE 2019, abstract O-179]
Total sperm count was 9 percent lower (95 percent confidence interval [CI], -25 to 10) among men whose fathers smoked daily compared with men whose fathers were non-smokers.
Similarly, sperm concentration was 8 percent lower (95 percent CI, -32 to 9) in men exposed to prenatal paternal daily smoking compared with those who were not.
In addition, men whose fathers smoked daily were 16 percent more likely to have a small testicle size compared with those whose fathers never smoked, although the association was not statistically significant.
“Our results did show an association with paternal smoking, but the effect of maternal smoking is much larger. If the mother, but not the father, smoked, the reduction was 26 percent for sperm concentration and 46 percent for sperm count. It’s certainly worse for the boys if the mother smokes,” said Tøttenborg. “Nevertheless, the circumstances in which the father smokes but the mother doesn’t is much more prevalent, so this is still very relevant for public health.”
Also, she added that even though the association between paternal smoking and semen quality is not as pronounced as other known risk factors, including pesticide exposure and urogenital disorders such as cryptorchidism, the magnitude still falls within the same range as smoking for the adult men.
According to the researchers, preconception paternal smoking can lead to epigenetic changes in the sperm genome, which can be passed on to the cells of the children. Although paternal smoking was assessed at week 16 of gestation, previous studies have shown that pre- and postconceptional smoking were highly correlated and thus, epigenetic changes may underlie the association between paternal smoking and semen quality.
“There have been previous studies investigating the association of paternal smoking with semen quality but these were small studies without information on key confounders,” said Tøttenborg.
“Our larger study does support these previous findings that paternal smoking is associated with sperm concentrations in male offspring independently of maternal smoking. We also found the association was independent of other preconceptional and prenatal risk factors for adult semen quality — including parental age, alcohol and caffeine consumption, prepregnancy BMI, and household occupational status,” she concluded.