Smoking and in vitro fertilization: a meta-analysis

Including our own data and seven relevant publications from the literature, this meta-analysis aimed to establish the influence of the status of female smokers on the clinical pregnancy rate after the first attempt at in vitro fertilization-embryo transfer (IVF-ET).

We started to collect information about our own patient's smoking habits in January 1996 to evaluate prospectively the influence on IVF success. Information regarding 799 patients (607 nonsmokers and 192 smokers) was obtained. Additionally we retrieved seven relevant publications from the unabridged MEDLINE 1982-1996. They were recalculated to first cycles, because from a biometrical point of view, only the results of the first IVF cycle are really well comparable, as the number of necessary IVF cycles always correlates with the number of pregnancies. These data were compared in the nonparametric sign test according to Dixon-Mood and calculated as relative success ratios, defined as the quotient of the probability of IVF-ET success of nonsmokers divided by that of smokers for each publication.

This meta-analysis, based on a total of 2314 first IVF-ET treatments, showed that almost twice as many IVF-ET cycles were needed for smokers as for nonsmokers to become pregnant. For the success quotient, we obtained a ratio of 1.79, with an associated 95% confidence interval of from 1.24 to 2.59. The total analysis shows, with a P value of less than 0.01, significantly higher pregnancy rates (21%) in nonsmokers compared to smokers (14%).

Based on the analyzed data there exists--from a statistical point of view--a significant negative effect on the chances of success for smokers to become pregnant compared to nonsmokers.