Smoking raises ectopic pregnancy risk

[Posted: Tue 03/07/2012 by Gillian Tsoi www.irishhealth.com]

Smoking increases the risk of ectopic pregnancy, according to scientists in the UK.

They discovered that cigarette smoke reduces the production of a fallopian tube gene known as "BAD", which helps explain the link between smoking and ectopic pregnancy.

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 this condition, which must be treated by abdominal surgery or, when the ectopic is small and stable, by injection of a drug called methotrexate.

Ectopic pregnancy results from 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 study, the researchers 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, and in particular with the BAD gene. In a further study the researchers showed that the BAD gene was reduced in the fallopian tube of women who smoked.

Changes in the production of BAD genes are seen in the uterus as it prepares for normal implantation of the embryo and early pregnancy. A reduction in this gene is normally seen in the cells of the uterus just before the embryo implants.

The study was led by Dr Andrew Horne and Dr Colin Duncan at the Medical Research Council (MRC) Centre for Reproductive Health in Edinburgh, UK.

The results of the research suggests that the reduced production of the BAD gene in the fallopian tube leads to an environment like that of the uterus, which encourages and allows ectopic pregnancy to occur.

"So our research," said Dr Lorne, "may in future help scientists find ways to prevent ectopic pregnancy, diagnosis it better, and treat it earlier."

He went on: "The research is exciting because it provides new scientific evidence to help understand why women who smoke are more likely to have ectopic pregnancies. It appears that smoking reduces the production of genes such as BAD, which are involved in the control of cell death and promote an environment in the Fallopian tube which is attractive to the developing embryo.

"The information gained from this study can also be applied to other conditions caused by smoking, and could help us prevent or treat them better in the long-term."

The study findings were presented at the annual meting of ESHRE (European Society of Human Reproduction and Embryology) in Istanbul.