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RESEARCH PRODUCT

Smoking habits of parents and male: female ratio in spermatozoa and preimplantation embryos

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BACKGROUND Previous observations have addressed a decreased male:female ratio associated with smoking. Our aim was to assess whether this effect is observed at the spermatozoa or at the early embryo development. METHODS We retrospectively assessed smoking intake habits of 56 couples included in our preimplantation genetic diagnosis (PGD) program. Three groups were established according to male or female cigarette consumption per day: non-smokers, smokers (1-19 cigarettes per day) and heavy smokers (> or =20 cigarettes per day). Fluorescence in-situ hybridization (FISH) was performed on ejaculated sperm samples to analyse chromosomes X and Y. On day 3, embryos were also analysed. Additionally, sperm samples from four heavy smoking and four non-smoking donors were prospectively analysed before and after capacitation. RESULTS FISH on spermatozoa revealed no statistical differences in the Y:X ratio between the three groups. However, in the PGD study, in male heavy smokers, the XY:XX embryo ratio was decreased compared with non-smokers (22:47 versus 80:71; P = 0.0057). The smoking condition of the female partner had no significant effect on embryo XY:XX ratio, but for non-smoking females with a heavy smoking partner, the ratio was decreased (P = 0.0018) compared with non-smoking males. In heavy smoking donors a decreased of Y:X ratio was observed after swim-up with a statistically significant difference of ratios (P = 0.021). CONCLUSIONS Smoking habits of males do not have an effect on the percentage of X- and Y-bearing spermatozoa on ejaculated samples. However, male heavy smokers produce an increased incidence of female embryos that could be related to an enrichment of X spermatozoa after swim-up in patients with high tobacco consumption.