Background: The risk associated with smoking has been studied for a long time in fertility epidemiology. This paper reviews the association between smoking and ectopic pregnancy (EP) using results collected in our previous studies. It provides arguments for a causal interpretation of this association.
Methods: Data came from three case-control studies performed between 1988 and 1996 and from the register of ectopic pregnancies in Auvergne (France) from 1992 to 1995. The methods are those classically used in the analysis of case-control studies.
Results: The risk of EP increased significantly with smoking (p < 0.01): the adjusted OR are 1.5 for 1-9 cigarettes a day, 2.0 for 10-19 cigarettes a day, and 2.5 for more than 20 cigarettes a day. The attributable risk of smoking ranged between 17% and 32% according to the study. Similarly, the risk of EP recurrence increased significantly with smoking (p < 0.02): after adjustment, OR = 1.3 for 1-9 cigarettes a day, OR = 1.5 for 10-19 cigarettes a day, and OR = 1.7 for more than 20 cigarettes a day. Finally, smoking was associated with the site of EP.
Conclusions: Thus there is a large body of arguments towards a causal relationship between smoking and EP. This provides additional arguments to persuade women to stop or to reduce smoking, especially hypofertile women.