Cigarette smoke reduces the production of a Fallopian tube gene known as "BAD", which helps explain the link between smoking and ectopic pregnancy. The finding, from scientists led by Drs Andrew Horne and Colin Duncan at the Medical Research Council (MRC) Centre for Reproductive Health in Edinburgh, UK, was described today at the annual meting of ESHRE (European Society of Human Reproduction and Embryology) in Istanbul.
Ectopic pregnancy - when the embryo implants outside the uterus and in the Fallopian tube - occurs in up to 2% of all pregnancies and is the most common cause of maternal death in early pregnancy. There is currently no way to prevent an ectopic pregnancy, and the condition must be treated by abdominal surgery or, when the ectopic is small and stable, by injection of a drug called methotrexate.
In presenting background information to the study, Dr Horne explained that ectopic pregnancy is the result of a combination of factors affecting the transport of the developing embryo from the Fallopian tube to the uterus and changes in the tubal environment which allow early implantation to occur. Smoking is known to be a major risk factor, but how smoking changes the environment of the Fallopian tube for an ectopic pregnancy to occur has so far remained largely unknown.
For the purpose of this study, Dr Horne's group first exposed cells from the Fallopian tube to a breakdown product of nicotine called cotinine. They then showed that cotinine had a negative effect on genes known to be associated with cell death (or apoptosis), and in particular with a gene called BAD. In a further study the researchers showed that BAD expression was reduced in the Fallopian tube of women who were smokers.
Dr Horne explained that changes in the production of BAD and related genes are seen in the uterus as it prepares for normal implantation of the embryo and early pregnancy. A reduction in the expression of BAD is normally seen in the cells of the uterus just before the embryo implants.