High-quality embryos maintain high pregnancy rates in passive smokers but not in active smokers.

This study assesses the effect of passive and active smoking on pregnancy rates after IVF with transfer of high-quality embryos. In a cohort study, women attending the IVF unit in 2006­2007 with favourable parameters for pregnancy (<38 years; less than three IVF cycles, transfer of two highest-grade embryos) grouped by smoking status were included. The cohort included 237 patients/cycles: 42 smokers, 195 non-smokers. The clinical pregnancy rate was significantly lower in smokers (35.7% versus 55.4%,P = 0.021, OR = 0.44 (95% CI 0.22­0.89)), even after conditional stratification on covariates (passive smoker, passive or partner smoker, age group). The live-birth rate was lower in smokers (28.6% versus 42.6%), but the difference was not statistically significant(OR = 0.54 (0.26­1.11)). Among non-smokers, there was no difference in pregnancy rate by passive or partner smoking. On logistic regression, variables predicting pregnancy were age <35 years (P = 0.008, OR = 2.58 (1.2­5.2)) and non-smoking (P = 0.003,OR = 3.47 (1.51­7.98)). In conclusion, transfer of high-quality embryos does not overcome the negative effect of active smoking on pregnancy rate in IVF treatment. The endometrium is apparently involved in the mechanism underlying IVF failure in smokers.