Effects of cigarette smoking and age on the maturation of human oocytes

We investigated whether cigarette smoking, measured by follicular fluidconcentrations of cotinine (a major metabolite of nicotine), affects thematurity of oocytes from women undergoing in-vitro fertilization (IVF) andembryo transfer. In 234 women, follicular fluid samples were assessed forcotinine and their 2020 oocytes were assessed for maturity stage. Data onindividual proportions of oocytes which were mature (OM) and werefertilized (OF) were analysed by regression in relation to age andfollicular fluid cotinine. OF gave an independent assessment of oocytematurity. Both age and follicular fluid cotinine entered the OM and OFregressions and were significant. The age-adjusted regression coefficientsfor log cotinine were positive; greater cotinine concentrations usuallyaccompanied greater OM and OF. The cotinine effect on OM was positive inyounger women, but it became negative (decreased OM with increasingcotinine concentrations) in older women (> or = 40 years). We furtherfound in older women an average reduction of approximately 50% in thenumber of mature oocytes; this reduced number was lower than the number ofembryos usually transferred. Smoking can reduce the number of matureoocytes even further, therefore risking a negative IVF-embryo transferoutcome. This may be the reason why the negative effects of smoking becomeclinically detectable in older women.