Effect of paternal smoking on pre-implantation embryonic development: a prospective cohort study.

Recent studies have failed to demonstrate the negative impact of male tobacco smoking on embryo development, raising the question of its actual implication on natural fecundity and assisted reproductive techniques outcomes. To assess the impact of paternal smoking on embryo development. In this prospective cohort study, 252 men from couples undergoing in vitro fertilisation (IVF) were included. Each patient was interviewed and took a carbon monoxide breath-test, creating three groups: non-smokers (n =113), former smokers (n =81) and active smokers (n =58). The Top-grade embryo ratio (primary endpoint), embryo morphokinetic parameters and clinical outcomes were assessed. In a multivariate analyses based on 1521 embryos, no significant difference was found in the top-grade embryo ratio between the groups. Tobacco smoking had no impact on clinical outcomes. Compared to non-smokers the time to the pronuclei fading (tPNf, P =0.006) and the time to the first embryonic cleavage (t2, P =0.002) were shorter in smokers, and the t2 was also slightly shorter in former smokers (P =0.045). No other differences were found in the morphokinetic parameters. Even if a few differences were observed in the first timing of embryonic events, this study did not highlight a major embryonic and clinical impact of the paternal smoking status. The results obtained here are reassuring towards IVF outcomes. As maternal smoking is highly controlled in the IVF patients in this study, we speculate that the sperm selection process may limit the adverse effects of tobacco consumption on embryo development.