Smoking could worsen the risk of ectopic pregnancy by increasing the levels of a protein in a woman's fallopian tubes, according to research.
Women who smoke are thought to be up to four times more likely to suffer an ectopic pregnancy, which occurs when the fertilised egg becomes implanted outside the womb, usually in the fallopian tubes. There are around 30,000 cases each year in the UK.
Researchers from the University of Edinburgh found that female smokers who had suffered an ectopic pregnancy had raised levels of a protein - PROKR1 - in their fallopian tubes, with a chemical in cigarette smoke called cotinine thought to be behind the rise.
The increased presence of the protein hinders the transfer of the egg to the uterus by preventing the muscles in the walls of the fallopian tubes from contracting, the research funded by the Wellbeing of Women charity found.
Dr Andrew Horne, from the University's Centre for Reproductive Biology, said: "While it may be easy to understand why inhalation of smoke affects the lungs, this shows that components of cigarette smoke also enter the bloodstream and affect seemingly unconnected parts of the body like the reproductive tract."