Perhaps lifestyle factors among cigarette smokers other than smoking account for this elevated risk. They are also likelier to have menstrual irregularity in middle age. Menopause tends to begin earlier in smokers. Thus, the reproductive window is longer in nonsmoking women. Clinical reports and evidence from animal experiments suggest that nicotine may be principally responsible for menstrual effects of smoking.
Cigarette smoking increases concentrations of the hormones epinephrine and vasopressin.
The Fallopian tubes are the most common site of ectopic pregnancy. If it is not detected early, ectopic pregnancy can result in fallopian-tube rupture and even death. Evidence from numerous studies suggests that cigarette smoking adversely affects the immune system. Some scientists have speculated that such changes may result in infertility through an increase in the frequency of fallopian-tube infection. Some of this evidence suggests that nicotine can prevent formation of cortical granules.